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Chairs
Francois Légaré Sylvain Charbonneau Institut national de la recherche scientifique University of Ottawa [email protected] [email protected]
André Staudte David M. Villeneuve National Research Council of Canada National Research Council of Canada [email protected] [email protected]
Indispensable help is gratefully acknowledged: Jennifer Vuong, Stephen Lee, Philippe-Thierry Douamba, Zack Dube
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David Villeneuve Group Leader, Attosecond National Research Council of Canada
Twenty-five year ago, in 1993, Paul Corkum published a landmark paper in Physical Review Letters. This paper provided a semi-classical picture of an electron, first removed from an atom by an intense laser field, then recolliding with its parent ion. This process is implicated in a number of strong-field processes, such as recollision excitation and high harmonic generation, and led to the field of attosecond science. Paul’s intuition, based upon previous work by many others, provided a simple picture that accurately explained many of the previous observations. This sole-author paper, P. B. Corkum, “Plasma perspective on strong field multiphoton ionization”, Phys. Rev. Lett. 71, 1994 (1993), has been so influential in many fields that it has been cited over 4500 times. This citation count puts the paper in the ranks of Nobel Prize winning material. The year, 2018, also marks another milestone, Paul Corkum’s 75th birthday. You would not know so, since his scientific output has increased dramatically since his “retirement” from the National Research Council 10 years ago. Paul founded the Joint Attosecond Science Laboratory, between the National Research Council and the University of Ottawa. JASLab has major facilities at both locations, along with a large number of students and postdocs who work under Paul’s direction. This symposium is a celebration of two things: The remarkable career of Paul Corkum, who has had such a profound impact on so many people; and the field of science that was launched in 1993, a field that so many of the symposium’s participants still work in.
David Villeneuve Ottawa, April 2018
4 Welcome Remarks
Duncan Stewart Director General, Security and Disruptive Technologies Research Centre National Research Council of Canada
E.W.R. Steacie, as president of the National Research Council of Canada in 1954, described with characteristic bluntness the difference between good and great research laboratories: “In a research organization, a few people make all the difference. If 5 per cent of the staff of a research laboratory are really first-rate, with imagination and initiative, all is well. […] The problem is to develop people of this type: to get behind them when they appear and give them the opportunity to develop themselves.” Steacie and his predecessor C.J. Mackenzie had recruited Gerhard Herzberg to the NRC in 1948 with exactly this aim. Both were particularly cognizant of the impact such people had in a government laboratory primarily preoccupied with longer range but applied research, and wrote to Herzberg: “We feel that not only will such a group engaged in fundamental research make valuable contributions to science but that such activity will maintain higher standards in the other more applied sections.” With that philosophy, Steacie and Herzberg built world-leading research efforts in photo- chemistry and spectroscopy at the NRC, efforts that delivered repeated major contributions to science and also, by proximity, to the NRC’s applied research. I suspect they might take wry pleasure in a symposium celebrating the spectroscopy of photo-chemistry! Most importantly, both would be enormously satisfied to see their vision of research excellence continued with such particular success by Paul Corkum, who by every possible standard is among the ‘few people that make all the difference’. Thank you for joining us in Canada at this symposium celebrating 25 years of re-collision physics.
Duncan Stewart Ottawa, May 2018
5 Keynote Speakers
Dr. Nemer holds a PhD in Chemistry from McGill University, and afterwards became a Professor of Pharmacology at the Université de Montréal. Subsequently, she became Professor and Vice-President, Research at University of Ottawa, and Director of the Molecular Genetics and Cardiac Regeneration Laboratory. Now she serves as Canada’s Chief Science Advisor. She is a Member of the Order of Canada, a fellow of the Academy of Sciences of the Royal Society
of Canada, Fellow of the American Academy of Arts and Mona Nemer Science, a Knight of the Ordre national du Québec, and a Chief Science Advisor Canada Knight of the French Republic’s ordre national du Mérite.
Dr. Tanguay received her Ph.D. in Parasitology from McGill University. From 2007-2011 she was the Assistant Deputy Minister for research, innovation, science and society with the Government of Québec, and from 2011-2015, the Vice-Rector, Research, Creation and Innovation at the Université de Montréal. She currently serves as the Vice-President of Emerging Techonlogies at the National Research Council of Canada, overseeing the Measurement Science and Standards Research Centre. She also oversees the Research Centre of Security and Geneviève Tanguay Disruptive Technologies, which is where NRC’s Vice-President Emerging Technologies, attosecond science is at home. National Research Council
Dr. John Alcock came to the National Research Council of Canada as a Postdoctoral Fellow in 1965 after obtaining his PhD from Oxford. He joined the continuing staff of the NRC in 1966 and from 1974 to 1990 he was head of the Laser & Plasma Physics Section in the Division of Physics. He is currently a Researcher Emeritus working in the Frequency and Time Section of the Measurement Science and Standards Research Centre. During his career, Dr. Alcock has worked in the areas of laser-produced plasmas, transverse discharge gas John Alcock lasers, ultra-short pulse generation, diode-pumped solid- National Research Council state lasers and high resolution spectroscopic measurements. He is a Fellow of the IEEE, the Optical Society and the Royal Society of Canada.
6 Session Chairs
Ladan Arissian Boris Bergues TJ Hammond National Research Council Max Planck Institute University of Ottawa of Canada of Quantum Optics [email protected] [email protected] [email protected]
Heide Ibrahim Ebrahim Karimi Matthias Kübel Institut national de la recherche Ludwig Maximilian University of University of Ottawa scientifique Munich [email protected] [email protected] [email protected]
Jérôme Levesque Moritz Meckel Andrew Shiner Department of National Defence, Baker & McKenzie Ciena Canada [email protected] [email protected] [email protected]
Murat Sivis Giulio Vampa Universität Göttingen Standford PULSE Institute [email protected] [email protected]
7 Presenters
Hiroshi Akagi Andre´ D. Bandrauk Kansai Photon Science Institute University of Sherbrooke [email protected] [email protected]
Pierre Berini Julien Bertrand University of Ottawa Laval University [email protected] [email protected]
Ravi Bhardwaj Robert Boyd University of Ottawa University of Ottawa [email protected] [email protected]
Thomas Brabec Paul Brumer University of Ottawa University of Toronto [email protected] [email protected]
Phil Bucksbaum Zenghu Chang Stanford University University of Central Florida [email protected] [email protected]
8 Presenters
´ See-Leang Chin Eric Constant Laval University Centre National de la Recherche [email protected] Scientifique [email protected]
Paul B. Corkum Jean-Claude Diels University of Ottawa University of New Mexico [email protected] [email protected]
Reinhard Dorner¨ Nirit Dudovich Institut fur¨ Kernphysik Weizmann Institute of Science Goethe Universitat¨ [email protected] [email protected]
Agapi Emmanouilidou Avner Fleischer University College London Tel Aviv University [email protected] fl[email protected]
Misha Yuri Ivanov Jean-Claude Kieffer Max Born Institut INRS [email protected] [email protected]
9 Presenters
Kyung-Taec Kim Matthias Kling Gwangju Institute of Science LMU Munich and Technology [email protected] [email protected] muenchen.de
Ferenc Krausz Max Plank Institute for Kevin F. Lee IMRA America, Inc Quantum Optics [email protected] [email protected]
Steve Leone Gerd Leuchs University of California, Max Planck Institute for the Berkeley Science of Light [email protected] [email protected]
Igor Litvinyuk Jon P. Marangos Griffith University Imperial College London i.litvinyuk@griffith.edu.au [email protected]
Katsumi Midorikawa Gerard´ Mourou RIKEN Center for Advanced Ecole´ Polytechnique Photonics gerard.mourou@ [email protected] polytechnique.edu
10 Presenters
Chang Hee Nam Hiromichi Niikura Gwangju Institute of Science Waseda University and Technology [email protected] [email protected]
Serguei Patchkovskii Gerhard Paulus Max Born Institut Helmholtz Institut Jena serguei.patchkovskii@mbi- [email protected] berlin.de
Jiahui Peng Michel Piche´ Huazhong University of Science Laval University and Technology [email protected] [email protected]
Claus Ropers Horst Schmidt-Bocking¨ Universitat¨ Gottingen¨ Goethe Universitat¨ [email protected] [email protected]
Marlan Scully Olga Smirnova Texas A&M Max Born Institut [email protected] [email protected]
11 Presenters
Michael Spanner Henrik Stapelfeldt National Research Council Aarhus University [email protected] [email protected]
Albert Stolow Donna Strickland National Research Council University of Waterloo [email protected] [email protected]
David M. Villeneuve Carlos Trallero National Research Council University of Connecticut david.villeneuve@nrc- [email protected] cnrc.gc.ca
Xu Wang Marc Vrakking China Academy of Engineering Max Born Institut Physics [email protected] [email protected]
Dirk Zeidler Carl Zeiss AG [email protected]
12
SCIENTIFIC PROGRAM
Tuesday, May 8 8:30-9:50 Tu1x Chair: Francois Légaré INRS-EMT, Canada 8:30 Tu10 Francois Légaré INRS-EMT, Canada Welcome Remarks 8:40 Tu11 David Villeneuve National Research Council, Canada
3.17 Up 9:10 Tu12 Ravi Bhardwaj University of Ottawa, Canada Recollision in large molecules 9:30 Tu13 Éric Constant University of Lyon, France Focusing of High Order Harmonics by XUV Wavefront Control 9:50-10:20 coffee break 10:20-12:00 Tu2x Chair: TJ Hammond University of Ottawa, Canada 10:20 Tu21 Jean-Claude Diels University of New Mexico, USA “Will the attometer resolution follow the attosecond?” 10:50 Tu22 Kyung Taec Kim Gwangju Institute of Science and Technology, Korea A Four-step Model for Coherent EUV Emission generated through Frustrated
Tunneling Ionization 11:10 Tu23 Igor Litvinyuk Griffith University Brisbane, Australia Attosecond Angular Streaking and Tunnelling Time in Atomic Hydrogen 11:30 Tu24 Chang Hee Nam Institute for Basic Science, Korea Attosecond Physics Research for 20 Years at KAIST 12:00-13:40 lunch break 13:40-15:30 Tu3x Chair: Ebrahim Karimi University of Ottawa, Canada 13:40 Tu31 Paul Brumer University of Toronto, Canada Fast Pulsed Lasers and Slow Steady-State Molecular Processes 14:10 Tu32 Robert Boyd University of Ottawa, Canada Paul Corkum and the Photonics Program at the University of Ottawa 14:40 Tu33 Julien Bertrand Laval University, Canada Time-Resolved Soft X-Ray Excitonics 15:00 Tu34 Michel Piché University of Laval, Canada Ultrafast Tightly Focused Vectorial Laser Beams: Application to particle
acceleration and microscopy 15:30-16:00 coffee break 16:00-18:00 Tu4x Chair: Andrew Shiner CIENA, Canada 16:00 Tu41 Marc Vrakking Max-Born-Institute, Germany Imaging Nuclear Wave Packets through Laser-Induced Electron Diffraction
in Photoexcited I2 Molecules 16:30 Tu42 Donna Strickland University of Waterloo, Canada Raman generation for intense single femtosecond pulse generation 17:00 Tu43 Jean-Claude Kieffer INRS-EMT, Canada Laser Wakefield Acceleration: A new tool for agriculture sector? 17:30 Tu44 Serguei Patchkovskii Max-Born-Institute, Germany Three-step factorization and essential molecular symmetries 20:00-21:30 poster session
14 Wednesday, May 9 8:30-9:50 We1x Chair: Boris Bergues Ludwig Maximilian University of Munich, Germany 8:30 We11 Jon Marangos Imperial College, United Kingdom
Extracting cation dynamics from HHG spectroscopy of complex molecules
9:00 We12 Hiromichi Niikura Waseda University, Japan
Phase-resolved imaging of an attosecond electron wavepacket
9:20 We13 Zenghu Chang University of Central Florida, USA
Attosecond X-rays driven by MIR lasers
9:50-10:20 coffee break
10:20-12:30 We2x Chair: Murat Sivis University of Goettingen, Germany 10:20 We21 Claus Ropers University of Goettingen, Germany
New Developments in Ultrafast Electron Imaging and Spectroscopy
10:50 We22 Dirk Zeidler Carl-Zeiss-Microscopy GmbH, Germany
High Speed Electron Microscopy
Huazhong University of Science and Technology, 11:10 We23 Jiahui Peng China Unveiling the Build-up Dynamics Mode-locking Process with Photonic Chromatography 11:30 We24 Pierre Berini University of Ottawa, Canada
Nonlinear plasmonic antennas
Max-Planck-Institute for the Science of Light, 12:00 We25 Gerd Leuchs Germany Quantum Limits of Coherent Beam Combining
12:30-14:00 lunch break
14:00-20:00 open discussions and breakout groups 20:00-21:30 poster session
15 Thursday, May 10
8:30-9:50 Th1x Chair: Matthias Kübel Ludwig Maximilian University of Munich, Germany 8:30 Th11 Gerhard Paulus Schiller University of Jena, Germany
Nanoscale non-invasive cross-sectional imaging with high-order harmonics
9:00 Th12 Nirit Dudovich Weizman Institute of Science, Israel
Photoionization probed via High Harmonic Generation Interferometry
9:20 Th13 Matthias Kling Ludwig Maximilian University of Munich, Germany
Attosecond photoemission delay in molecules around giant resonances
9:50-10:20 coffee break
10:20-12:00 Th2x Chair: Moritz Meckel Baker & McKenzie International, Germany 10:20 Th21 Phil Bucksbaum Stanford University, USA
Clocking electrons in strong-field ionization
10:50 Th22 Henrik Stapelfeldt Aarhus University, Denmark
Laser-induced Coulomb explosion of molecules: Structure, dynamics, alignment
11:10 Th23 Avner Fleischer Tel Aviv University, Israel
Recollision-less High Harmonic Generation
11:30 Th24 Reinhard Dörner Goethe University of Frankfurt, Germany
Electrons at the end of the tunnel
12:00-13:30 lunch break
Th3x Chair: Giulio Vampa Stanford University, USA
13:30 Th31 Xu Wang China Academy of Engineering Physics, China
Virtual Detector Theory for Strong-Field Atomic Ionization
14:00 Th32 Agapi Emmanouilidou University College London, United Kingdom
Controlling electron-electron correlation in frustrated double ionization of molecules with orthogonally polarized two-color laser fields 14:30 Th33 Thomas Brabec University of Ottawa, Canada
The 3-step recollision process in laser driven solids
15:00 Th34 Michael Spanner National Research Council, Canada High Harmonic Generation is the Sound of the 80s
15:30-16:00 coffee break
16:00-18:00 Th4x Chair: Ladan Arissian National Research Council, Canada University of California Berkeley & Lawrence 16:00 Th41 Steve Leone Berkeley National Lab, USA Attosecond Probing of Core-Level Dynamics in Solids
16:30 Th42 Horst Schmidt-Böcking Goethe University of Frankfurt, Germany
Zepto-second Pump & Probe Experiments with Ion-Beam Methods
17:00 Th43 See-Leang Chin Laval University, Canada
Filament and Corona induced precipitation in a cloud chamber
17:30 Th44 Albert Stolow University of Ottawa, Canada
The Life It Brings: Molecules in Laser Fields
19:00-22:00 Banquet with keynotes
Mona Nemer Chief Science Advisor Canada
Geneviève Tanguay Vice-President Emerging Technologies, NRC, Canada
John Alcock National Research Council, Canada
16 Friday, May 11 8:30-9:50 Fr1x Chair: Jérôme Levesque Defence Research and Development Canada 8:30 Fr11 Olga Smirnova Max-Born-Institute, Germany
On subtle difference between left and right: inducing and probing ultrafast chiral dynamics 9:00 Fr12 Kevin Lee IMRA America, Inc., USA
Passively Stable Coherent Combination of Ultrafast Fiber Lasers
9:20 Fr13 André Bandrauk University of Sherbrooke, Canada
Circular Polarization in Attosecond Phenomena and Applications
9:50-10:20 coffee break
10:20-12:00 Fr2x Chair: Heide Ibrahim INRS-EMT, Canada 10:20 Fr21 Katsumi Midorikawa Riken Center for Advanced Photonics, Japan
High Energy Mid-Infrared Lasers by DC-OPA for Creating Intense Attosecond Light Bullets Nat'l Institutes for Quantum and Radiological Science 10:50 Fr22 Hiroshi Akagi and Technology, Japan Molecular frame angular distribution of tunnel ionization probability from molecular orbitals: HCl and ethanol cases 11:10 Fr23 Carlos Trallero University of Connecticut, USA
Towards strong field science with longer wavelengths
11:30 Fr24 Gérard Mourou Haut collège of École Polytechnique, France
Science of High Energy, Single-Cycled Laser
12:00-13:30 lunch break
13:30-15:30 Fr3x Chair: David Villeneuve National Research Council, Canada 13:30 Fr31 Misha Ivanov Max-Born-Institute, Germany
Strong field spectroscopy of electron dynamics: from laser filaments to strongly correlated solids 14:00 Fr32 Marlan Scully Texas A&M University & Princeton University, USA
From Black Holes to Black Mold
14:30 Fr33 Ferenc Krausz Max-Planck-Institute of Quantum Optics, Germany
Next-generation attosecond metrology
15:00 Fr34 Paul Corkum University of Ottawa, Canada
Looking forward after 25 years of re-collision
15:30 coffee and departure
17 Abstracts
ABSTRACTS – PRESENTATIONS
3.17 Up ...... 22 Recollision in large molecules ...... 23 Focusing of High Order Harmonics by XUV Wavefront Control ...... 24 Will the attometer resolution follow the attosecond? ...... 25 A Four-step Model for Coherent EUV Emission generated through Frustrated Tunneling Ionization ...... 26 Attosecond Angular Streaking and Tunnelling Time in Atomic Hydrogen ...... 27 Attosecond Physics Research for 20 Years at KAIST ...... 28 Fast Pulsed Lasers and Slow Steady-State Molecular Processes ...... 29 Paul Corkum and the Photonics Program at the University of Ottawa ...... 30 Time-Resolved Soft X-Ray Excitonics ...... 31 Ultrafast Tightly Focused Vectorial Laser Beams: Application to particle acceleration and microscopy . 32
Imaging Nuclear Wave Packets through Laser-Induced Electron Diffraction in Photoexcited I2 Molecules ...... 33 Raman generation for intense single femtosecond pulse generation ...... 34 Laser Wakefield Acceleration: A new tool for agriculture sector? ...... 35 Three-step factorization and essential molecular symmetries ...... 36 Extracting cation dynamics from HHG spectroscopy of complex molecules ...... 37 Phase-resolved imaging of an attosecond electron wavepacket ...... 38 Attosecond X-rays driven by MIR lasers ...... 39 New Developments in Ultrafast Electron Imaging and Spectroscopy ...... 40 High Speed Electron Microscopy ...... 41 Unveiling the Build-up Dynamics Mode-locking Process with Photonic Chromatography ...... 42 Nonlinear plasmonic antennas ...... 43 Quantum Limits of Coherent Beam Combining ...... 44 Nanoscale non-invasive cross-sectional imaging with high-order harmonics ...... 45 Photoionization probed via High Harmonic Generation Interferometry ...... 46 Attosecond photoemission delay in molecules around giant resonances ...... 47 Clocking electrons in strong-field ionization ...... 48 Laser-induced Coulomb explosion of molecules: Structure, dynamics, alignment ...... 49 Recollision-less High Harmonic Generation ...... 50 Electrons at the end of the tunnel ...... 51 Virtual Detector Theory for Strong-Field Atomic Ionization ...... 52
18 Controlling electron-electron correlation in frustrated double ionization of molecules with orthogonally polarized two-color laser fields ...... 53 The 3-step recollision process in laser driven solids ...... 54 High-Harmonic Generation is the Sound of the 80s ...... 55 Attosecond Probing of Core-Level Dynamics in Solids ...... 56 Zepto-second Pump & Probe Experiments with Ion-Beam Methods ...... 57 Filament and Corona induced precipitation in a cloud chamber ...... 58 The Life It Brings: Molecules in Laser Fields ...... 59 On subtle difference between left and right: inducing and probing ultrafast chiral dynamics ...... 60 Passively Stable Coherent Combination of Ultrafast Fiber Lasers ...... 61 Circular Polarization in Attosecond Phenomena and Applications ...... 62 High Energy Mid-Infrared Lasers by DC-OPA for Creating Intense Attosecond Light Bullets ...... 63 Molecular frame angular distribution of tunnel ionization probability from molecular orbitals: HCl and ethanol cases ...... 64 Towards strong field science with longer wavelengths ...... 65 Science of High Energy, Single-Cycled Laser ...... 66 Strong field spectroscopy of electron dynamics: from laser filaments to strongly correlated solids ...... 67 From Black Holes to Black Mold ...... 68 Next-generation attosecond metrology ...... 69 Looking forward after 25 years of re-collision ...... 70
ABSTRACTS – POSTERS Tuesday, May 8, 2018 All-optical interferometric probing of attosecond electronic wavepackets ...... 72 Attosecond-Resolved Photoionization of Chiral Molecules ...... 73 Phase- and Intensity-Resolved Measurements of Above Threshold Ionization by Few-Cycle Pulses ...... 74
Probing the Phase Transition in VO2 Using Few-Cycle 1.8 μm Pulses ...... 75 Extreme focusing by axisymmetric systems: The inverse problem ...... 76
Ionization Dynamics in Ultrafast Strong Field Ionization of C60 ...... 77 Designing Chirped Pulse Amplifiers on the Perspective of Time Lens Imaging ...... 78 Self-guided HHG for single-shot spectroscopy in the water window ...... 79 Temporal Characterization of Multi-cycle Laser Pulses using the Tunneling Ionization Method ...... 80 Prompt Dissociation of Metastable CO2+ in a Dimer ...... 81 Strong field stabilization and the excitation of neutral atoms in COLTRIMS ...... 82 High-power, high-energy femtosecond laser systems for scientific and industrial applications ...... 83 A Real-Space Perspective on High Harmonic Generation in Solids ...... 84 Background-Free Measurements of Autoionizing State Lifetimes in Krypton with Extreme Ultraviolet Wave Mixing ...... 85
19 Study and Applications of LIFT based mass spectrometry using ultrafast laser pulses ...... 86 Two-cycle, 2.5 TW pulse generation at 1.8 μm via Frequency domain Optical Parametric Amplification87 Controlled energy deposition in micromachining by using two femtosecond laser pulses ...... 88 Light amplification by seeded Kerr instability ...... 89
ABSTRACTS – POSTERS Wednesday, May 9, 2018 Where Do They Go? Proton Migration in Hydrocarbons ...... 92 Holographic Measurement of Time-dependent Optical Fields ...... 93 Selectivity of electronic coherence and attosecond ionization delays in strong-field double ionization .... 94 Streak Camera for Strong-Field Ionization ...... 95 Insulator-to-semimetal transition of dielectric crystals under strong optical fields ...... 96 + Testing the role of recollision in N2 air lasing ...... 97 Amplitude and phase transfer in Fourier-domain nonlinear optics ...... 98 Spatial properties of high harmonic beams from plasma mirrors ...... 99 High Harmonics Sources for Probing Ultrafast Optical Demagnetization in Multilayer Films ...... 100
XUV Transient Absorption of Pre-aligned N2 molecules ...... 101 Compression of femtosecond electron pulses using tightly focused terahertz waves ...... 102 IR Peak Power & Average Power scaling via (FOPA) ...... 103 High Harmonic Generation in Tailored Solids ...... 104 Strong-Field-Induced Vibronic Coupling ...... 105 Is there a gauge-independent formulation of interband and intraband currents in solids? ...... 106 15 W, few-cycle and ultra-stable mid-IR OPCPA ...... 107 Visualization of multiple bands structures in solids ...... 108 Disentangling Intracycle Interferences in Photoelectron Momentum Distributions Using Orthogonal Two- Color Laser Fields ...... 109 Generation of Few-Cycle UV pulses Synchronized with Attosecond XUV Pulses ...... 110
20
ABSTRACTS – PRESENTATIONS
Tu11
3.17 Up David Villeneuve Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, 100 Sussex Drive, Ottawa ON K1A 0R6 Canada [email protected]
The second stage of Paul Corkum’s remarkable scientific career began in 1993 with the publication of his landmark sole-author paper on the role of recollision in strong field ionization [1]. This paper and the concepts behind it created the field of recollision physics and led to new research areas such as attosecond science. The paper’s title illustrates the breadth of Paul’s knowledge. He started out in the field of theoretical statistical mechanics. During his interview for a postdoctoral position at NRC, his claim to be able to rebuild a car engine landed him a job as an experimental plasma physicist. I will trace the trajectory of Paul’s exceptional career as a scientist and as a mentor to many people.
References [1] P. B. Corkum, Plasma perspective on strong field multiphoton ionization, Phys. Rev. Lett. 71, 1994 (1993).
22 Tu12
Recollision in large molecules
M. Alsaawy, V.R. Bhardwaj University of Ottawa, Ottawa, ON, K1N 6N5 [email protected] Electron recollision played a key role in technological development of high harmonic and attosecond pulse generation resulting in major scientific breakthroughs. This coherent and well- controlled process has also provided valuable information about atoms, molecule and solids with unprecedented time resolution. As we celebrate the 25th anniversary of the birth of recollision physics, I will present experimental results that challenge our current understanding of this process when extended to larger systems such as C60 and chiral molecules.
23 Tu13
Focusing of High Order Harmonics by XUV Wavefront Control
L. Quintard1, V. Strelkov2, J. Vabek1, O. Hort1†, A. Dubrouil1‡, D. Descamps1, F. Burgy1, C. Péjot1, E. Mével1, F. Catoire1, and E. Constant1,3* 1Université de Bordeaux, CNRS, CEA, Centre Laser Intenses et Applications (CELIA), 43 rue P. Noailles, 33400 Talence, France 2A M Prokhorov General Physics Institute of Russian Academy of Sciences, 38, Vavilova Street, Moscow 119991, Russia. Moscow Institute of Physics and Technology (State University), 141700 Dolgoprudny, Moscow Region, Russia 3Université de Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière (ILM), rue Ada Byron, 69622 Villeurbanne, France †present address: ELI Beamlines Project, Institute of physics, Czech Academy of Sciences, Praha 8, Czech Republic ‡present address: Femtoeasy, Femto Easy SAS, parc scientifique Laseris 1 , 33114 Le Barp, FRANCE *[email protected]
The spatial profile of XUV beams obtained via high order harmonic generation (HHG) with few mJ energy femtosecond laser pulse in a gas jet is studied. We show that the spatial properties of these XUV beams depend strongly on harmonic generation conditions and especially on the position of the generating medium. We show that the spatial profile of the XUV beam can be finely controlled without XUV optics. This evolution is analyzed with an analytical model that considers the propagation of XUV Gaussian beams generated with well-known intensity profile and wave front curvature in a plane following the model described in [1]. This approach reproduces closely our experimental observations and allows us to infer the XUV beam characteristics during propagation for both short and long quantum paths. We observe that the XUV beams have spatial properties that changes significantly with the harmonics order and quantum path. Harmonic beams exhibit foci which positions depend on the specific conditions of HHG. These foci are generally not localized at the position of the fundamental beam waist and their position can vary significantly with the harmonic order. The relative XUV foci shift can even be larger than the XUV confocal parameter. In return, the observed foci shift can strongly affect the XUV spectral width at focus. This work also demonstrates that XUV beams can be emitted as converging beams under specific conditions and we observe experimentally this direct XUV focusing by inducing a spatial asymmetry [2] during the generation process and observing its impact in the far field spatially resolved harmonic spectra. Our observations show that XUV beams can be directly focused without any XUV optics by controlling their wavefront during the harmonic generation process. We observe that these XUV foci can be located at arbitrarily large distances after the generating medium. This focusing property implies that intense XUV field can be obtained with coherently-focused harmonics and we discuss how such order-dependent XUV foci positions is compatible with broadband XUV irradiation and attosecond science. References [1] F. Catoire et al., “Complex structure of spatially resolved high-order-harmonic spectra”, Phys. Rev. A 94, 063401 (2016). [2] H. Vincenti and F. Quére, “Attosecond Lighthouses: How To Use Spatiotemporally Coupled Light Fields To Generate Isolated Attosecond Pulses”, Phys. Rev. Lett. 108, 113904 (2012)
24 Tu21
Will the attometer resolution follow the attosecond?
Jean-Claude Diels CHTM, University of New Mexico, Albuquerque, NM 87106
One might think that, with the space-time analogy, the attometer era would come nearly simultaneously with the attosecond. As the attosecond scale was reached through accurate phase control of the optical cycle of a fs pulses, attometer resolution can be reached through subwavelength control of the electric field in space. In both cases, ultrashort pulses are required. But the analogy stops there. Precise measurements of the optical path requires active laser cavities, coupled to highly dispersive passive resonators. Instead large vacuum technology, the highest spatial sensitivity calls for miniaturization, down to integrated circuit lasers and nano-fabrication techniques.
25 Tu22
A Four-step Model for Coherent EUV Emission generated through Frustrated Tunneling Ionization
Kyung Taec Kim1,2*, Hyeok Yun1, Je Hoi Mun1, Sung In Hwang1, Seung Beom Park1, Igor A. Ivanov1, and Chang Hee Nam1,2 1Center for Relativistic Laser Science, IBS, Gwangju 61005, Korea 2Department of Physics and Photon Science, GIST, Gwangju 61005, Korea *[email protected]
Coherent extreme ultraviolet (EUV) emission can be obtained through high-harmonic generation (HHG) which is well explained by the three-step model [1]. First, an electron can tunnel out through the potential barrier of an atom exposed to the strong laser field. Second, the liberated electron is accelerated and driven back to the parent ion. Finally, the kinetic energy gained in the strong laser field is converted to the radiation when the electron recombines to the parent ion. The periodic repetition of the three-step process is HHG that has been actively studied for the last few decades. The high-harmonic radiation resulting from the strong-field interaction has become an essential tool not only as a light source for applications but also as a signal that contains the information on the interaction processes, which has opened up the field of attosecond science and high-harmonic spectroscopy [2]. There is a similar strong field process known as frustrated tunneling ionization (FTI) in which an electron liberated in strong laser field recombines to the excited states of an atom [3]. The FTI process can be explained by the four-step model. First, an electron tunnels out from an atom at the peak of a laser field. Second, it oscillates in the strong laser field. The electron ionized at the peak of the laser field has a zero kinetic energy at the end of the laser pulse. Third, the zerokinetic-energy electron recombines to the excited states of the atom. Finally, the coherent EUV radiation is emitted by free induction decay. Here we demonstrate the experimental observation of the coherent EUV emission generated through the FTI. The four-step theoretical model clearly explains the dependences on the ellipticity and the carrier-envelope-phase of the laser pulses. In addition, we demonstrate the control of the propagation direction of the emission by employing the attosecond lighthouse technique. The coherent property of the FTI emission can be utilized in many applications, and offers new opportunity in ultrafast spectroscopy.
References [1] P. B. Corkum, “Plasma perspective on strong field multiphoton ionization,” Phys. Rev. Lett. 71, 1994–1997 (1993). [2] P. B. Corkum et al., “Attosecond science,” Nat. Phys. 3, 381–387 (2007). [3] T. Nubbemeyer et al., “Strong-Field Tunneling without Ionization,” Phys. Rev. Lett. 101, 233001 (2008).
26 Tu23
Attosecond Angular Streaking and Tunnelling Time in Atomic Hydrogen
U. Satya Sainadh1, Han Xu1, Xiaoshan Wang2, Atia-Tul-Noor1, William C. Wallace1, Nicolas Douguet3†, Alexander Bray4, Igor Ivanov5, Klaus Bartschat3, Anatoli Kheifets4, R. T. Sang1 & I. V. Litvinyuk1 1Australian Attosecond Science facility, Centre for Quantum Dynamics, Griffith University, Australia 2School of Nuclear Science & Technology, Lanzhou University, Lanzhou, China 3Department of Physics and Astronomy, Drake University, Des Moines, Iowa, USA 4Research School of Physics and Engineering, The Australian National University, Canberra, Australia 5Centre for Relativistic Laser Science, Institute for Basic Science, Gwangju, Korea [email protected]
The ongoing debate about the value, meaning and interpretation of ‘tunnelling time’ was reignited recently with the development of ultrafast lasers and attosecond metrology1, which gave experimental access to the attosecond (1 as = 10-18 s) domain. In particular, the ‘attoclock’2 technique was used to probe the attosecond dynamics of electrons tunnelling out of atoms interacting with intense laser fields. Although the initial attoclock measurements3-5 hinted at instantaneous tunnelling, later experiments6,7 claimed to have measured finite tunnelling times. These measurements were performed with multi- electron atoms with no accurate theoretical modelling available. Atomic hydrogen (H), the simplest atomic system with a single electron, can be ‘exactly’ (subject only to numerical limitations) modelled and thus acts as a convenient benchmark for both accurate experimental measurements and calculations8-10. Here we report the first attoclock experiment performed on H using a ‘Reaction Microscope’11 (REMI) and 770 nm, 6 fs pulses (FWHM) with peak intensities of 1.65 - 3.9 ×1014 W/cm2. We find that our experimentally determined offset angles of the photoelectrons are in excellent agreement with accurate 3D-TDSE simulations performed using the Coulomb potential with our experimental pulse parameters. The same simulations with a short-range Yukawa potential result in zero offset angles for all intensities. We conclude that the offset angle measured in the attoclock experiments originates entirely from electron scattering by the long-range Coulomb potential with no contribution from tunnelling time delay. Thus we confirm that, in atomic H, tunnelling is instantaneous within our experimental and numerical uncertainty. This puts an upper limit of 1.8 attoseconds on possible delays due to tunnelling. This result in effect rules out all commonly used ‘tunnelling times’12 from being interpreted as time spent by an electron under the barrier.
References [1] Hentschel, M. et al. Nature 414, 509-513 (2001). [2] Eckle, P. et al. Nature Physics 4, 565-570 (2008). [3] Eckle, P. et al. Science 322, 1525-1529 (2008). [4] Pfeiffer, A. N. et al. Nature Physics 8, 76-80 (2012). [5] Pfeiffer, A. N., Cirelli, C., Smolarski, M. & Keller, U. Chem. Phys. 414, 84-91 (2013). [6] Landsman, A. S. et al. Optica 1, 343-349 (2014). [7] Camus, N. et al. Phys. Rev. Lett. 119, 023201 (2017). [8] Kielpinski, D., Sang, R. & Litvinyuk, I. J. Phys. : 7, 204003 (2014). [9] Wallace, W. et al. Phys. Rev. Lett. 117, 053001 (2016). [10] Khurmi, C. et al.. Phys. Rev. A 96, 013404 (2017). [11] Dörner, R. et al. Phys. Rep. 330, 95-192 (2000). [12] Zimmermann, T. et al. Phys. Rev. Lett. 116, 233603 (2016).
27 Tu24
Attosecond Physics Research for 20 Years at KAIST
Chang Hee Nam Center for Relativistic Laser Science, Institute for Basic Science, Gwangju 61005, Korea; Department of Physics and Photon Science, GIST, Gwangju 61005, Korea [email protected]
At the occasion to celebrate the 25th anniversary of recollision physics a recollection of the attosecond physics research performed at KAIST for 20 years is presented. An attosecond physics lab at KAIST was established from scratch by developing a high power femtosecond laser and constructing a flat-field XUV spectrometer [1]. Based on the homemade laser and diagnostics the generation and characterization of high harmonics could be initiated [2]. In 1999 the Coherent X-ray Research Center was launched, which prompted further developments of attosecond physics research. The coherent control process of high harmonic generation was demonstrated by manipulating the chirp of a femtosecond laser [3], and strong boost of harmonic signal was achieved by applying two-color laser pulses [4]. In addition, rigorous temporal characterization of attosecond harmonic pulse trains was successfully realized by applying the FROG CRAB technique [5], and the attosecond chirp compensation was demonstrated by making use of material dispersion [6]. More recently high harmonic sources have been applied to explore the dynamics and structure of atoms and molecules [7,8]. All these achievements could be made possible thanks to the hard works of former KAIST graduate students.
References [1] Y. H. Cha et al., “Generation of a broad amplified spectrum in a femtosecond terawatt Ti:sapphire laser using a long wavelength injection method,” J. Opt. Soc. Am. B 16, 1220 (1999); I. W. Choi et al., “Space-resolving flat-field XUV spectrograph system and its aberration analysis with wave front aberration,” Appl. Opt. 36, 1457 (1997). [2] H. J. Shin et al., “Generation of Nonadiabatic Blueshift of High Harmonics in an Intense Femtosecond Laser Field,” Phys. Rev. Lett. 83, 2544-2547 (1999). [3] D. G. Lee et al., “Coherent control of high-order harmonics with chirped femtosecond laser pulses,” Phys. Rev. Lett. 87, 243902 (2001). [4] I J. Kim et al., “Highly efficient high-harmonic generation in an orthogonally polarized two-color laser field,” Phys. Rev. Lett. 94, 243901 (2005). [5] K. T. Kim et al., “Complete temporal reconstruction of attosecond high-harmonic pulse trains,” New J. Phys. 12, 083019 (2010); D. H. Ko et al., “Attosecond chirp compensation over broadband high-order harmonics to generate near transform-limited 63-as pulses,” New J. Phys. 12, 063008 (2010). [6] K. T. Kim et al., “Single sub-50-attosecond pulse generation from chirp-compensated harmonic radiation using material dispersion,” Phys. Rev. A 69, 051805(R) (2004); K. T. Kim et al., “Self-Compression of Attosecond High-order Harmonic Pulses,” Phys. Rev. Lett. 99, 223904 (2007). [7] K. T. Kim et al., “Amplitude and phase reconstruction of electron wave packets for probing ultrafast photoionization dynamics,” Phys. Rev. Lett. 108, 093001 (2012). [8] H. Yun et al., “Resolving multiple molecular orbitals using two-dimensional high-harmonic spectroscopy,” Phys. Rev. Lett. 114, 153901 (2015).
28 Tu31
Fast Pulsed Lasers and Slow Steady-State Molecular Processes
Paul Brumer Department of Chemistry, and Center for Quantum Information and Quantum Control University of Toronto, Toronto, Ontario, Canada M5S 3H6 [email protected]
Numerous molecular processes in nature, such as photosynthesis or vision, are initiated by the absorption of light. Such processes are often studied in the laboratory with ultrafast pulsed laser techniques and display time-dependent molecule dynamics characterized by oscillatory coherences. By contrast, natural processes are initiated by excitation with stationary incoherent (e.g. solar) radiation, leading to a dramatically different, time-independent, steady state response. We discuss, based upon formal and computational approaches, the relationship and differences between ultrafast laser induced dynamics and ultraslow steady state rates (e.g., see references [1,2,3,4]). In addition, we propose an experimental means of obtaining the incoherent excitation results using shaped pulsed laser light [5].
References [1] A. Dodin, T. V. Tscherbul and P. Brumer, “Coherent Dynamics of V-type Systems Driven by Time-Dependent Incoherent Radiation”, J. Chem. Phys. 145, 244313/1-12 (2016). [2] L.A. Pachon, J.D. Botero and P. Brumer “Open System Perspective on Incoherent Excitation of Light Harvesting Systems”, J. Phys. B: At. Mol. Opt. Phys. 50, 184003/1-13 (2017). [3] T.V. Tscherbul and P. Brumer, “Excitation of Biomolecules with Incoherent Light: QuantumYield of the Photoisomerization of Model Retinal”, J. Phys. Chem. A 118, 3100-3111 (2014). [4] S. Axelrod and P. Brumer, Manuscript in preparation. [5] A. Chenu and P. Brumer, “Transform-Limited-Pulse Representation of Excitation with Natural Incoherent Light”, A. Chenu and P. Brumer, J. Chem. Phys. 144, 044103/1-6 (2016).
29 Tu32
Paul Corkum and the Photonics Program at the University of Ottawa
Robert W. Boyd Department of Physics, University of Ottawa, Ottawa ON Canada [email protected]
In this talk I highlight the enormous role that Paul has played on the establishment of the world-class photonics program of the University of Ottawa (UO). Paul first established his own superb program at NRC; much of the present Symposium highlights the accomplishments of this program. Later on, Paul was able to convince UO to make a major investment in the field of photonics. Part of this plan included Paul accepting a faculty position at UO. Another part included the commitment to construct the ARC building (the state-of-the-art research laboratory building that houses the photonics program) and also to write a proposal to the Canadian government to hire a Canada Excellence Research Chair (CERC) in the area of Quantum Photonics. This proposal was successful, and the competition to become the CERC chairholder was won by the present author. Paul helped me to negotiate the package to bring me here. This package included faculty slots for three junior professors, all of whom have now been hired. Moreover, Paul played a key role on the team that convinced the Max Planck Society to establish a Max Planck Centre at UO based on the theme of Extreme and Quantum Photonics. My summary premise is that Paul has played a key role in the enormous growth of the photonics program at UO. I for one am extremely grateful for all that Paul has done for me.
30 Tu33
Time-Resolved Soft X-Ray Excitonics
Julien B. Bertrand, A. Moulet, T. Klostermann, A. Guggenmos, N. Karpowicz, E. Goulielmakis Laval University and Center for Optics, Photonics and Lasers, 2375 de la Terrasse Street, Quebec (QC), Canada, G1V 0A6 [email protected]
Attosecond Physics explores ways to follow and control matter with unprecedented temporal resolution (1 attosecond= 10-18 s.). Strong laser fields used to apply forces on the sub-cycle timescale, together with the availability of tabletop attosecond soft x-ray pulses, now open avenues for direct time-resolving ultrafast dynamics on the unexplored attosecond timescale [1,2]. In this first attosecond pump - attosecond probe experiment, an isolated 107 eV attosecond pulse initiates an Auger decay followed by an attosecond broadband (250-1100 nm) optical pulse. The observable is the soft x-ray absorption spectrum as a function of pump-probe delay. A first experiment in krypton atoms allows us to model the effect of the optical probe as a gate of the Auger electronic dipole, a universal analog to the frequency- resolved optical gating technique [3]. Applying our attosecond x-ray absorption near-edge spectroscopy (AXANES) to the L-edge of fused silica enables us to directly observe and control sub-femtosecond core- excitons in solids, laying the foundation of soft x-ray excitonics [4].
Fig. Retrieval of soft x-ray—induced core-exciton dynamics in SiO2. (A) Measured. (B) Reconstructed attosecond pump-probe differential absorption spectrogram.
References [1] J. B. Bertrand et al., Nature Physics 9, 174 (2013). [2] S. R. Leone et al., Nature Photonics 8, 162 (2014). [3] R. Trebino, FROG, Kluwer Academic Publishers, Boston (2002). [4] A. Moulet, J. B. Bertrand et al., Science 357, 1134-1138 (2017).
31 Tu34
Ultrafast Tightly Focused Vectorial Laser Beams: Application to particle acceleration and microscopy
Michel Piché1, Simon Robitaille1, Jeck Borne1, Shanny Pelchat-Voyer1, Louis Thibon1,2, Yves De Koninck1,2, and Simon Thibault1 1Centre d’optique, photonique et laser, Université Laval, 2375 de la Terrasse, Québec, Québec G1V 0A6, Canada 2Centre de Recherche CERVO, Institut universitaire en santé mentale de Québec, Université Laval, 2601 de la Canardière, Québec, Québec G1J 2G3, Canada [email protected]
The beams generated by laser systems are most often specified as either linearly polarized, circularly polarized or non-polarized. Under conditions of tight focusing, the state of polarization of an initially linearly polarized laser beam is not preserved in the focal volume: new electric and magnetic field components develop along the longitudinal axis and the orthogonal transverse axis. Laser beams propagating in free space can also have states of polarization similar to the electromagnetic modes of metallic waveguides. Properly designed spatial light modulators can be used to transform linearly polarized laser beams into vectorial laser beams with radial polarization (transverse magnetic modes) or azimuthal polarization (transverse electric modes). This presentation will provide an overview of our work on the theoretical description of ultrafast tightly focused laser beams and the application of such beams to particle acceleration and high-resolution microscopy. Exact solutions for the electromagnetic field structure of monochromatic vectorial laser beams have been obtained using a method combining the complex source/sink model with the Hertz vector potentials [1]. Extension to ultrafast beams was made possible using a Poisson spectrum which reduces to a Gaussian spectrum in the slowly-varying envelope approximation. These exact solutions were used to model the acceleration of charged particles by the longitudinal field of tightly focused radially polarized laser pulses. Using this formalism, it has been shown that electrons could be accelerated to relativistic speed by sufficiently short and intense laser pulses [2]. Experiments realized with the 1.8-μm, two-cycle beam line at ALLS have validated the scheme [3]. Recent calculations have indicated that electron pulses that undergo stretching during propagation can be compressed by high power terahertz pulses. Azimuthally polarized laser beams can be focused into narrow donut beams. The size of their central dark one can be as small as ~ λ/4. This feature was exploited to enhance the resolution of a confocal microscopy beyond diffraction limit; a resolution below 100 nm was achieved in biological samples [4-5]. Engineering the focal spot is a crucial issue that can be addressed using an inverse method where the targeted solution defines the profile of the incident laser beam.
References [1] A. April, “Ultrashort, strongly focused laser pulses in free space,” in Coherence and Ultrashort Pulse Laser Emission, F. J. Duarte, ed., InTech, 355–382 (2010). [2] V. Marceau, C. Varin et al., “Femtosecond 240-keV electron pulses from direct acceleration in a low-density gas,” Phys. Rev. Lett. 111, 224801 (2013). [3] S. Payeur, S. Fourmaux et al., “Generation of a beam of fast electrons by tightly focusing a radially polarized ultrashort laser pulse,” Appl. Phys. Lett. 101, 041105 (2012). [4] H. Dehez, M. Piché et al., “Resolution and contrast enhancement in laser scanning microscopy using dark beam imaging,” Opt. Express 21, 15912-15912-15925 (2013). [5] L. Thibon, L. E. Lorenzo et al., ”Resolution enhancement in confocal microscopy using Bessel-Gauss beams,” Opt. Express 25, 2162-2177 (2017).
32 Tu41
Imaging Nuclear Wave Packets through Laser-Induced Electron Diffraction in Photoexcited I2 Molecules F. Brauße, A. Rouzée, M. J. J. Vrakking Max-Born-Institut, Max-Born-Straße 2a, 12489, Berlin, Germany
The strong-field ionization of atoms and molecules has been intensively investigated over the last three decades. An electron released by a strong laser field can be accelerated away from its parent ion before it is driven back. As it returns to its parent ion, re-collision eventually occurs leading to additional processes such as laser-induced electron holography and diffraction [1], non-sequential double ionization [2] or high-order harmonic generation [3,4]. The latter is responsible for the emission of ultrashort bursts of XUV and (soft) X-ray radiation with pulse durations reaching the attosecond timescale, which in turn can be used to investigate in “real time” ultrafast electron dynamics in atoms and molecules [5]. One of the main consequences of elastic re-scattering in the laser field is the appearance of a “re-collision plateau” in the photoelectron spectrum. Under certain conditions, the photoelectron angular distributions (PADs) corresponding to this plateau region contain diffraction features that can be used to image the molecular structure. This idea was experimentally benchmarked in Ar and Xe [6] before it was applied by Corkum and co-workers in N2 and O2 [7] and is often referred to as laser-induced electron diffraction (LIED) [8,9]. Here, we present a first attempt to observe bond-breaking and vibrational wave-packet dynamics of a simple diatomic molecule using this concept. PADs from strong-field ionization of I2 molecules by an intense 1.3 µm laser pulse were recorded following photoexcitation by either a 710 nm or a 550 nm pump laser pulse. In the former case, photoexcitation is leading to molecular dissociation, whereas in the latter a vibrational wave packet is formed. Using a model based on the quantitative re-scattering theory [10], the differential scattering cross section (DCS) is directly extracted from the PADs and is compared to ab- initio calculations using ePolyScat [11,12]. Surprisingly, we observe that the DCS is dominated by a strong shape resonance at the equilibrium geometry that disappears as the molecular bond stretches, in good agreement with the theoretical prediction.
References [1] Y. Huismans et al., Science 331, 61 (2011). [2] S. Larochelle, A. Talebpour, and S. L. Chin, Journal of Physics B-Atomic Molecular and Optical Physics 31, 1201 (1998). [3] A. McPherson, G. Gibson, H. Jara, U. Johann, T. S. Luk, I. A. McIntyre, K. Boyer, and C. K. Rhodes, J. Opt. Soc. Am. B 4, 595 (1987). [4] M. Ferray, A. L. Huillier, X. F. Li, L. A. Lompre, G. Mainfray, and C. Manus, Journal of Physics B: Atomic, Molecular and Optical Physics 21, L31 (1988). [5] F. Krausz and M. Ivanov, Reviews of Modern Physics 81, 163 (2009). [6] M. Okunishi, T. Morishita, G. Prumper, K. Shimada, C. D. Lin, S. Watanabe, and K. Ueda, Physical Review Letters 100 (2008). [7 M. Meckel et al., Science 320, 1478 (2008). [8] C. I. Blaga, J. Xu, A. D. DiChiara, E. Sistrunk, K. Zhang, P. Agostini, T. A. Miller, L. F. DiMauro, and C. D. Lin, Nature 483, 194 (2012). [9] B. Wolter et al., Science 354, 308 (2016). [10] Z. J. Chen, A. T. Le, T. Morishita, and C. D. Lin, Physical Review A 79 (2009). [11] F. A. Gianturco, R. R. Lucchese, and N. Sanna, Journal of Chemical Physics 100, 6464 (1994). [12] A. P. P. Natalense and R. R. Lucchese, Journal of Chemical Physics 111, 5344 (1999).
33 Tu42
Raman generation for intense single femtosecond pulse generation
Donna Strickland, Zujun Xu, Abdullah Rahnama and Jongsoo Lee Department of Physics and Astronomy, University of Waterloo, 200 University Avenue W, Waterloo, ON N2L 3G1 [email protected] Multi-frequency Raman generation can be used to produce a sufficiently wide spectrum to generate a train of single femtosecond pulses [1]. Although this technique cannot compete in temporal resolution with attosecond pulse generation techniques, it is a very efficient nonlinear process and could lead to intense ultrashort pulse generation. In the transient regime, where the pump pulses are of the same duration as the coherence time of the Raman transition, it has been shown that the individual Raman orders are spectrally broadened [2], which could lead to shorter pulse trains and so higher peak intensities. We are currently investigating the temporal profile of the individual anti-Stokes orders using second order Frequency Resolved Optical Gating (FROG). We have determined that the broadened order is comprised of two chirped pulses. There is not enough information from the second order FROG to uniquely determine the spectral shift and temporal delay between the two pulses. We are currently investigating cross-FROG measurements between the pump and the first anti-Stokes order. In this talk we will discuss the role of two-photon Rabi splitting of the Raman levels leading to the second chirped pulses and the implications for generating intense single femtosecond pulses.
References [1] A.V. Sokolov, et al. “Femtosecond Light Source for Phase-Controlled Multiphoton Ionization”, Phys. Rev. Lett. 87, 033402 (2001) [2] H. Yan, et al., “Effect of Two-photon Stark Shift on the Multi-Frequency Ramand Spectra” Appl. Sci, 4, 390-401 (2014)
34 Tu43
Laser Wakefield Acceleration: A new tool for agriculture sector?
Jean Claude Kieffer1*, Sylvain Fourmaux1, Emil Hallin2 1INRS-EMT, 1650 blvd Lionel Boulet, J3X1S2 Varennes, Qc, Canada 2Global Institute for Food Security, 110 Gymnasium Place, University of Saskatchewan, Saskatoon, SK, S7N 4J8 Canada *[email protected]
We presented previously [1,2] the potential impact of ultrafast laser-based X-ray sources. We will discuss in this talk the generation of high throughput hard X-ray radiation (>20 keV) by Laser Wakefield Acceleration (LWFA) process [3], which could allow a paradigm shift in a wide range of applications [4]. We demonstrated in 2011 at INRS [5], and simultaneously similar results were obtained at U. of Michigan [6], that one phase contrast hard x-ray image could be produced in one X-ray pulse with a reasonable signal to noise ratio. This is opening a new route for fast 3D imaging of various objects [7]. These X-ray sources have also unique duration characteristics, since they are as short as the optical driving laser pulses, offering extraordinary potential for femtosecond molecular imaging and Warm Dense Matter probing [8]. We upgraded over the past two years the INRS high peak power laser facility from 200 TW (5 J, 30 fs) to 600 TW (11 J, 18 fs). The experimental programs have been restarted at the beginning of 2017 in the continuity of our previous scientific directions, i.e. high intensity laser-matter interaction and ultrafast X-ray sources. In this talk we will present and discuss experiments realized with our new laser facility, with a particular emphasis on the generation of ultrafast bright hard X-rays. We will present the characterization of our upgraded LWFA betatron beam line coupled to our new laser system. Results have been obtained with 5 J in 20 fs pulses on gas target with an incident intensity of 1019 W/cm2 and with a 2.5 Hz repetition rate. After the initial self- focusing, the laser intensity modulates corresponding to successive self-focusing and defocusing periods of the laser along its propagation. The control of this key non-linear process on long distance has resulted in the generation of very bright emission of betatron radiation. The parameters of the LWFA driven betatron X-ray source are a repetition rate of 2.5 Hz, a photon yield of 2x109 photons/0:1% bandwidth/sr/shot at 40 keV (which gives an average power of 5x109 photons/0:1% bandwidth/sr/s), a critical energy around 40 keV, an effective X-ray source size of 1 μm, a divergence of 50 mrads x 50 mrads, an X-ray beam pointing stability and an X-ray energy stability in the 2% rms range. Diagnostics of the interaction include the measurements of accelerated electron (spectrum, charge), of the femtosecond dynamics of the laser propagation inside the gas jet (synchronized probe beam and ultrafast shadowgraphy, Thomson imaging), of the quality of the laser beam (phase, intensity distribution, contrast, prepulses, duration, spectrum, energy on target, stability), and of the X-ray beam parameters (spectrum, Yield, divergence…) We will present our funded program (through CFREF program) in developing high throughput X-ray phase contrast screening system based on our LWFA X-ray sources for plant imaging through an initiative led by the Global Institute for Food Security (GIFS) at the U of Saskatchewan that aims to elucidate that part of the functional that maps specific environmental inputs onto specific plant phenotypes. The goals of our imaging project are i) to determine the optimized working point for X-ray plant imaging with high throughput laser-based X-ray system and ii) to prepare a detailed technical design of a laser-based betatron system for dedicated 3D plant imaging [9]. We will discuss the progresses we have realized over the past year in optimizing and controlling the 2.5 Hz LWFA betatron X- ray source and doing X-ray phase contrast imaging of complex objects including wheat fusarium, canola seeds and plants, hydraulic structures in poplar stems and roots systems inside soils of different compositions. The comparison of laser-based (LWFA at INRS) and synchrotron (CLS at Saskatoon) imaging technologies used with the same kind of plants and samples demonstrates that the agile small scale imaging laser-based system captures all the key features on a screening time scale compatible with the crop plant breeding context. These very encouraging results indicate that the laser-based technology could be in a very near future a unique new tool for the agriculture sector.
References [1] C. Kieffer et al, Appl. Phys. B 74, S75 (2002). [2] J.C. Kieffer et al, 19th International Conference and School on Quantum Electronics: Laser Physics and Applications, edited by Tanja Dreischuh, Sanka Gateva, Albena Daskalova, Alexandros Serafetinides, Proc. of SPIE Vol. 10226, 1022612 (2017). [3] S. Corde et al, Rev. Mod. Phys. 85, 1 (2013). [4] J.C. Kieffer et al, SPIE Newsroom, 10.1117/2.1201610.006713 (December 2016). [5] S. Fourmaux et al, Opt. Lett. 36, 2426 (2011). [6] S. Kneip et al, Appl. Phys. Lett. 99, 093701 (2011). [7] J. Wenz et al, Nature Communications 6:7568 doi: 10.1038/ncomms8568 (2015). [8] M. Mo et al, Rev. Sci. Instrum. 84, 123106 (2013) and Phys. Rev. E, 95, 053208 (2017). [9] J.C. Kieffer et al, Proceedings of SPIE, Vol. 10239, 1023906 (2017) doi:10.1117/12.2263951.
35 Tu44
Three-step factorization and essential molecular symmetries
F. Schell, T. Bredtmann, C.P. Schulz, S. Patchkovskii*, M.J.J. Vrakking, and J. Mikosch Max-Born-Institut für nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2A, 12489 Berlin, Germany [email protected]
The three-step model [1] is the cornerstone of our understanding of many processes involving atoms and molecules interacting with intense, long-wavelength laser fields. In this model, the three steps (ionization, propagation under the influence of the laser field, and interaction upon recollision) can be treated as conceptually independent and factorizable. Treatments based on the factorization idea have been remarkably successful in describing phenomena ranging from high-harmonics generation to non- sequential double ionization to laser-induced electron diffraction (LIED). In the simplest three-step model of LIED the total probability I of observing a high- energy rescattered photoelectron is given by a product of three factors: I=Q*R*S, where S is the probability of ionization, R is the probability of return, and Q is the probability of high-angle scattering. A recent experiment at the Max-Born Institute simultaneously measured both I and S for two distinct ionization channels, as a function of the molecular-frame laser polarization direction θ [2]. The resulting rescattering probability Q*R=I/S is strongly channel-dependent, both in shape an in the overall magnitude, even though both the propagation and the rescattering steps are expected to be only weakly dependent on the electronic state of the cationic core. The channel- and orientation-dependence of the rescattering probability is connected to the essential symmetries of the underlying molecular wavefunctions, which are carried over to the transverse structures of the continuum wavepackets. We explore these effects numerically, by solving the time-dependent Schrödinger equation, and analytically, within the strong-field approximation (SFA). We identify two physical mechanisms affecting the rescattering probability. In the first mechanism, presence of a molecular (anti-)symmetry element causes the majority of direct photoelectrons to be emitted with non- zero transverse velocities, reducing the return probability R. The overall probability of observing a rescattered photoelectron however remains factorizable. This effect is already included in some LIED theories (e.g. [3]). The second mechanism operates close to field-conserved molecular (anti-)symmetry elements, where the returning wavepacket carries an essential tranverse phase structure in the interaction region. The resulting rescattering probability is sensitive to the spatial structure of both the ionization and scattering matrix elements, and is non-factorizable.
References [1] P.B. Corkum, “Plasma Perspective on Strong-Field Multiphoton Ionization”, PRL 71, 1994 (1993). [2] F. Schell, T. Bredtmann, et al, “Molecular Orbital Imprint in Laser-Driven Electron Recollision”, Sci Adv, in print (2018). [3] T. Morishita and O.I. Tolstikhin, “Adiabatic theory of strong-field photoelectron momentum distributions near a backward rescattering caustic”, PRA 96, 053416 (2017).
36 We11
Extracting cation dynamics from HHG spectroscopy of complex molecules
D.R.Austin, A.S.Johnson, D.Wood, F.McGrath, P.Hawkins, M.Ivanov*, O.Smirnova*, A.Harvey*, Z.Masin*, S.Patchkovskii*, J.P.Marangos† Physics Department, Imperial College, London, SW 2AZ, UK, *Max Born Institute, Berlin, Germany † [email protected]
The ultrafast evolution of a molecule following ionisation in a strong field is a key problem in attosecond science. The dynamics, involving coupled multi-electronic and nuclear quantum states, are at the frontier of our understanding in chemical physics with importance to laser interaction with matter and to concepts of controlling chemical dynamics with light. One method that has advanced our understanding is the use of high harmonic generation spectroscopy (HHGS). An early demonstration of HHGS was the retrieval of fast nuclear dynamics using the chirp encoding of the HHG signal in H2 and CH4 [1]. Typically HHGS is applied as a multi-dimensional technique with the HHG spectrum recorded as a function of controllable parameters such as molecular axis alignment angle, laser wavelength and laser intensity. The electron hole dynamics of certain small molecules (carbon dioxide, iodoacetylene) have been fully retrieved and interpreted via HHGS using controllable molecular alignment, laser wavelength and intensity [2,3,4]. Methods of molecular alignment are not, however, available for the vast majority of polyatomic molecules and we must seek alternatives to maximise the information that can be extracted from HHGS. We demonstrate a HHGS multidimensional method where we measure just harmonic spectra as a function of laser intensity (figure 1 (a)) that allows robust retrieval of the dynamical factors through the chirp encoding in the HHG spectrum. This is suitable for application to a much larger set of polyatomic molecules. Using this for substituted benzenes, along with standard analysis procedures, we have retrieved the nuclear autocorrelation function in the benzene cation (decay time ~ 3 fs) (figure 1(b)) and the nuclear autocorrelation function and relative phase of a superposition of electronic states created by strong field ionization by an 1800 nm field in the fluorobenzene cation.
Figure 1(a) Harmonic spectrum vs intensity Figure 1(b) Retrieval of nuclear dynamics in benzene
References [1] Baker S, et al Science 312, 424 (2006) [2] Smirnova O, et al Nature 460, 972 (2009). [3] Haessler et al, Nat. Phys. 6, 200 (2010). [4] Kraus P.M. et al, Science 350, 790 (2015)
37 We12
Phase-resolved imaging of an attosecond electron wavepacket
H. Niikura1, P. Hockett2, S. Patchkovskii3, M.J.J. Vrakking3 and D. Villeneuve2 1Department of Applied Physics, Waseda University, 3-4-1 Okubo Shinjyuku, Tokyo, Japan. 2National Research Council of Canada, 100 Sussex Dr., Ottawa, ON, Canada. 3Max-Born-Institute, Max Born Straße 2A, D-12489 Berlin, Germany. [email protected]
Imaging and controlling an electronic wave function is one of the major aims for the study of ultra-fast dynamics in atoms and molecules. For complete characterization of the wave function, both the amplitude and phase distribution over the position or momentum is required. Recently, we have observed an almost pure f-wave ionized from neon by an attosecond pulse train consisting of odd-number harmonics (XUV pulse) and an IR laser pulse1. Fig. 1(a) shows the observed photoelectron momentum distribution. A clear six-fold structure was observed and identified as an f-wave with a magnetic quantum number (m) of 0. The isolation of m=0 is unusual since in general removing one electron from the outermost 2p-electron of neon can produce three states with different magnetic quantum numbers. We have proposed as mechanism where the dominant production of the f-wave with m=0 results from a two-color (XUV+IR) two-photon resonant ionization process through a Stark-shifted 3d-level of neon. Next, we resolve the phase of the photoelectron wave by adding a one-photon, XUV-one ionization process using even high-harmonics to the afore-mentioned two-photon process. The one-photon process can produce an s-wave (and/or a d-wave) in the ionization continuum. In our case, an s-wave is predominantly generated and the coherent overlap between the s-wave and the f-wave resolves the phase of the f-wave (Fig. 1 (b)). Changing the delay between the XUV and the IR highlights another set of lobes. By measuring the photoelectron distribution as a function of the XUV-IR delay and comparing them to a model calculation, we have obtained a complete characterization of the amplitude and phase of the partial waves involved in the ionization process. Our method allows us to measure the relationship between the phase and the momentum of the ejected photoelectron. In future, it will be extended to other atoms or electronic states where fast electron dynamics can occur.
Fig.1. (a) Measured photoelectron momentum distributions for neon. (b) Phase-resolved image of the (almost pure) f-wave at different XUV and IR delay times (T). The polarization direction of the XUV and IR laser pulses is vertical in the figure.
References [1] D. Villeneuve, P. Hockett, M.J.J. Vrakking and H. Niikura, “Coherent imaging of an attosecond electron wave packet,” Science 356, 1150- 1153 (2017).
38 We13
Attosecond X-rays driven by MIR lasers
Zenghu Chang Institute for the Frontier of Attosecond Science and Technology, CREOL and Department of Physics, University of Central Florida, Orlando, Florida 32816, USA [email protected]
Few-cycle Ti:Sapphire lasers centered at 800 nm have been working horses for attosecond pulse generation for the last 17 years. The spectral range of isolated attosecond pulses with sufficient photon flux for time-resolved pump-probe experiments has been limited to extreme ultraviolet (10 to 150 eV). It was demonstrated in 2001 that the cutoff photon energy of high harmonic spectrum could be extended by increasing the center wavelength of driving lasers [1], as predicted by the three-step model. In recent years, mJ level, two-cycle, carrier-envelope phase stabilized lasers at 1.6 to 2.1 micron have been developed by compressing pulses from Optical Parametric Amplifiers with gas-filled hollow-core fibers or by implementing Optical Parametric Chirped Pulse Amplification (OPCPA) techniques. When a 3 mJ, 12 fs laser at 1.7 m laser was used to implement polarization gating, isolated soft X-rays in the water window (280-530 eV) were generated in our laboratory. The number of X-ray photons in the 120– 400 eV range per laser shot is comparable to that generated with Ti:Sapphire lasers in the 50 to 150 eV range [2]. When the width of the polarization gate was set to less than one-half of the laser cycle, a soft X-ray supercontinuum was generated. Isolated X-ray pulses with 53 as duration were characterized by attosecond streaking measurements [3]. Such ultrabroadband light sources are now being used in time- resolved X-ray absorption near edge structure measurements for studying charge dynamics in atoms and molecules. High power mid-infrared lasers centered at even longer wavelengths, 2.5 m and 8 m are being developed in our laboratory to push the attosecond X-rays into the keV photon energy range [4]. This work has been supported Army Research Office (W911NF-14-1-0383, W911NF-15-1-0336); Air Force Office of Scientific Research (FA9550-15-1-0037, FA9550-16-1-0013, FA9550-17-1- 0499); the DARPA PULSE program by a grant from AMRDEC (W31P4Q1310017). This material is also based upon work supported by the National Science Foundation under Grant Number (NSF Grant Number 1506345).
References [1] Bing Shan, Zenghu Chang, “Dramatic extension of the high-order harmonic cutoff by using a long-wavelength driving field”, Physical Review A 65, 011804(R) (2001). [2] Jie Li et al., “Polarization gating of high harmonic generation in the water window”, Applied Physics Letters 108, 231102 (2016). [3] Jie Li et al., “53-attosecond X-ray pulses reach the carbon K-edge”, Nature Communications 8, 186 (2017). [4] Yanchun Yin et al., “Towards terawatt sub-cycle long-wave infrared pulses via chirped optical parametric amplification and indirect pulse shaping”, Scientific Reports 8, 45794 (2017).
39 We21
New Developments in Ultrafast Electron Imaging and Spectroscopy
Claus Ropers University of Göttingen, Germany [email protected]
Novel methods in time-resolved electron microscopy, diffraction and spectroscopy promise unprecedented insight into the dynamics of structural, electronic and magnetic processes on the nanoscale. A key to the realization of such technologies is the generation of high-quality beams of ultrashort electron pulses. In this talk, our recent development of imaging and spectroscopy using localized electron emitters will be discussed. Specifically, two approaches employing high-coherence electron pulses from nanotips will be presented, namely Ultrafast Low-Energy Electron Diffraction (ULEED) and Ultrafast Transmission Electron Microscopy (UTEM). ULEED allows for the study of structural dynamics with high temporal resolution and ultimate surface sensitivity [1-2], while UTEM combines femtosecond [3-6] and even attosecond [7] resolution with the imaging and spectroscopy capabilities of an electron microscope.
MCP and phosphor screen
gun
electrons
photo- emission pulse pump pulse sample
Figure: Two complementary approaches to the study of ultrafast dynamics in solids, at surfaces and nanostructures: Ultrafast Low-energy electron diffraction (ULEED, left) probes structural dynamics at surfaces with electron pulses at kinetic energies of 20-200 eV. Ultrafast transmission electron microscopy (UTEM, right) allows for ultrafast imaging, diffraction and spectroscopy of thin films and nanostructures using high-energy electron pulses (100-200 keV).
References [1] M. Gulde et al., "Ultrafast low-energy electron diffraction in transmission resolves polymer/graphene superstructure dynamics", Science 345, 200 (2014). [2] S. Vogelgesang et al., "Phase ordering of charge density waves traced by ultrafast low-energy electron diffraction", Nat. Phys. 14, 184–190 (2018). [3] A. Feist et al., “Ultrafast transmission electron microscopy using a laser-driven field emitter: Femtosecond resolution with a high coherence electron beam”, Ultramicroscopy 176, 63 (2017). [4] A. Feist et al., “Nanoscale diffractive probing of strain dynamics in ultrafast transmission electron microscopy”, Struct. Dyn. 5, 014302 (2018). [5] A. Feist, K. E. Echternkamp, J. Schauss, S. V. Yalunin, S. Schäfer, and C. Ropers, “Quantum coherent optical phase modulation in an ultrafast transmission electron microscope”, Nature 521, 200 (2015). [6] K. E. Echternkamp, A. Feist, S. Schäfer, and C. Ropers, “Ramsey-type phase control of free electron beams”, Nature Phys. 12, 1000 (2016). [7] K. E. Priebe, C. Rathje, S. V. Yalunin, T. Hohage, A. Feist, S. Schäfer, and C. Ropers, “Attosecond Electron Pulse Trains and Quantum State Reconstruction in Ultrafast Transmission Electron Microscopy”, Nat. Phot. 11, 793 (2017).
40 We22
High Speed Electron Microscopy
Dirk Zeidler Carl Zeiss Microscopy GmbH, Carl-Zeiss-Straße 22, 73447 Oberkochen, Deutschland [email protected]
Since their invention, scanning electron microscopes (SEMs) have advanced in a number of aspects, such as increasing their resolution, improving their usability through digitization and miniaturization, and adding detection schemes such as energy- or wavelength-dispersive X-ray spectrometry. The data acquisition rates of SEMs, though, while maintaining both nanometer resolution and high signal-to-noise ratio (SNR), have not seen huge improvements. The maximum scan speed of any conventional SEM is limited by the electron dose per pixel required to generate a desired minimal SNR at a given spot size: (i) reducing dwell time per pixel while retaining SNR requires increasing the beam current, which leads to increased Coulomb interactions between the electrons, thereby blurring the electron beam, and (ii) efficient detectors for secondary electrons in an SEM cannot be operated at arbitrarily high rates. Multiple beam SEMs circumvent these two restrictions, as they (i) distribute the charge over a large volume, thus reducing Coulomb effects, and (ii) use one detector for each beam, yielding a much higher total detector bandwidth at relatively low detector rates per beam. The details of our setup have been described elsewhere [1]. Figure 1 summarizes the basic principle of operation.
Figure 1. Visualization of the basic principle of operation. Multiple primary electron beams (blue) within a single column are scanned in parallel over a sample. One dedicated detector per secondary electron beam (green) enables parallel detection of the signals from all beams. For simplicity, only 7 beams are shown in this sketch. A video of the operation principle is available on the internet at https://p.widencdn.net/fvzxio/principle_MultiSEM.
We will give a synopsis on multiple beam scanning electron microscopy approaches, demonstrate the single column, multiple beam technology and its scalability, and present an overview of its latest application results.
References [1] A. L. Eberle et al, Journal of Microscopy 259 (2015), p. 114-120.
41 We23
Unveiling the Build-up Dynamics Mode-locking Process with Photonic Chromatography
Jiahui, Peng School of Optical and Electronic Information, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, China, 430074 [email protected]
Femtosecond lasers have been employed to expand the boundary of experimental methods, such as ultrafast dynamics, optical clocks and other precise measurements [1-3]. However, femtosecond mode- locked pulses evolve from diverse initial conditions, like long pulses, noises and continuous waves. The underlying physics picture has not been clearly outlined because conventional optical equipment is not suitable for resolving such fast, non-repetitive and transient events. Recently, real time single-shot measurements such as dispersion Fourier transform (DFT) have enriched ultrafast characterization [4-6]. Dispersion elements are utilized to separate different optical frequency components with different group delays, which is a technique we nickname as Photonic Chromatography with the inspiration from Paul Corkum. The spectrum is then mapped onto the temporal waveform, and then the high speed temporal optical detection enables the possibility to observe transient events, including the start-up of mode-locking [5]. Here, with photonic chromatography, we present our characterization on the build-up dynamics of femtosecond fiber lasers. We hope this observation will help people to understand the start-up mechanism of mode-locking and to build mode-locked lasers with better stability.
Fig.1 Repetition signals obtained with fast photo diode(a); Spectra obtained with Photonic Chromatography by roundtrips (b); Experiment setup of our Photonic Chromatography measurement (c).
References [1] Zewail, A. H. "Laser femtochemistry." Science 242.4886: 1645-1653. (1988) [2] Chou, Chin-Wen, et al. "Optical clocks and relativity." Science 329.5999: 1630-1633. (2010) [3] Udem, Th., et.al. . "Optical frequency metrology." Nature 416.6877: 233–237. (2002) [4] Goda, K., et.al. "Dispersive Fourier transformation for fast continuous single-shot measurements." Nature Photonics 7.2: 102–112. (2013) [5] Herink, G., et al. "Real-time spectral interferometry probes the internal dynamics of femtosecond soliton molecules." Science 356.6333: 50- 54. (2017) [6] Ryczkowski, P., et al. "Real-time full-field characterization of transient dissipative soliton dynamics in a mode-locked laser." Nature Photonics: 1. (2018) [5] Herink, G., et al. "Resolving the build-up of femtosecond mode-locking with single-shot spectroscopy at 90 MHz frame rate." Nature Photonics 10.5: 321–326. (2016)
42 We24
Nonlinear plasmonic antennas
Behnood Ghamsari1,2, Maryam Al-Shehab1,2, Anthony Olivieri1,2, Pierre Berini1,2,3 1School of Electrical Engineering and Computer Science, University of Ottawa, 800 King Edward St., Ottawa, Canada 2Centre for Research in Photonics, University of Ottawa, 25 Templeton St., Ottawa, Canada, 3Department of Physics, University of Ottawa [email protected]
Nanometallic structures are essential to the conversion of light to surface plasmon-polaritons (SPPs) localized to ultra-small volumes. Such structures can provide highly enhanced fields, strong confinement and high surface sensitivity, so they are of interest in many applications, including plasmon-enhanced nonlinear optics [1-5], which is of interest in this paper. Fig. 1 (Left) gives a sketch of a structure of interest [1]. The device comprises an array of rectangular Au nanoantennas of length l, width w and thickness t, on graphene on SiO2/Si. The antennas are arranged over the surface following pitch p and q.
Fig. 1. (Left) Sketch of a plasmonic antenna array comprising Au nanorods of thickness t, width w and length l, on a graphene layer on SiO2/Si. (Centre) SEM image of a fabricated array. (Right) Normalised reflectance response of arrays of nanoantennas of differing length. Fabrication is achieved via e-beam lithography, evaporation and lift-off on CVD grown graphene [1]. The structures are shown in the SEM image of Fig. 1 (centre). Nanoantenna arrays such as these are very useful to enhance light-graphene interaction, as can be surmised from the strong resonances observed from reflectance measurements obtained for nanoantennas on graphene, shown in Fig. 1 (right) [4]. Plasmon-enhanced nonlinear processes of interest in this system include Raman scattering [1-3], where the nanoantennas are spectrally-aligned with a Stokes wavelength of graphene; under this scenario, single-antenna enhancement factors of over 100× have been observed. Also of interest is plasmon- enhanced high-harmonic generation via re-collision radiation, as recently observed in Si [5].
References [1] Ghamsari, B. G., Olivieri, A., Variola, F., Berini, P., “Enhanced Raman scattering in graphene by plasmonic resonant Stokes emission,” Nanophotonics 3, 363, 2014 [2] Ghamsari, B. G., Olivieri, A., Variola, F., Berini, P., “Frequency Pulling and Lineshape Broadening in Graphene Raman Spectra by Resonant Stokes Surface Plasmon Polaritons,” Phys. Rev. B 91, 201408, 2015 [3] Ghamsari, B. G., Berini, P., “Surface Plasmon Near-Field Back-Action and Displacement of Enhanced Raman Scattering Spectrum in Graphene,” J. Opt. 18, 074008, 2016 [4] Al-Shehab, M., Ghamsari, B. G., Berini, P., (manuscript in preparation). [5] Vampa, G., Ghamsari, B. G., Siadat Mousavi, S., Hammond, T. J., Olivieri, A., Lisicka-Skrek, E., Naumov, A., Villeneuve, D. M., Staudte, A., Berini, P., Corkum, P. B., “Plasmon-enhanced high harmonic generation from silicon,” Nature Physics 13, 659 (2017).
43 We25
Quantum Limits of Coherent Beam Combining
Gerd Leuchs1,2,3,4, Christian R. Müller1,2, Florian Sedlmeir1,2, Sourav Chatterjee1,2, and Christoph Marquardt1,2 1Max Planck Institute for the Science of Light, Staudtstraße 2, 91058 Erlangen, Germany 2Department of Physics, University of Erlangen-Nuremberg, Staudtstraße 7/B2, 91058 Erlangen, Germany 3Institute for Applied Physics, Russian Academy of Sciences, 603950 Nizhny Novgorod, Russia 4Max Planck–University of Ottawa Centre for Extreme and Quantum Photonics, 25 Templeton Street, Ottawa, Ontario K1N 6N5, Canada [email protected]
Coherent beam combining (CBC) refers to the process of generating a bright output beam by merging independent input beams with locked relative phases. This technique allows to extend the power scaling of fibre amplifier systems beyond the current limitations caused by thermal mode instabilities [1, 2], but can also be considered for quantum-limited coherent input beams. The noise profile of the combined beam depends crucially on the relative optical phases in the combining step, where the precision of phase locking is fundamentally limited by quantum uncertainty. We report the first quantum mechanical noise limit calculations for coherent beam combining, and we compare our results to the performance of a quantum-limited amplifier. Ideally, the output power in CBC is the sum of the powers of the individual input beams and thus an integer multiple of the single beam power. In this respect CBC can be seen as a kind of amplifier with discrete steps in the gain factor. The signal-to-noise ratio of a quantum-limited linear amplifier operating in the high gain regime is reduced by at least 3dB due to the underlying quantum uncertainties [3], and the excess noise variance is proportional to the gain factor. The noise scaling in CBC is fundamentally different. In adding up multiple input beams, the individual phase fluctuations, stemming from the limited phase-locking accuracy, are progressively averaged out. With increasing number of combined beams the excess noise variance is approaching an asymptotic value such that the ratio between the noise variance and the mean intensity is continuously decreasing. This can serve as a basis to extend the power range of nearly shot noise limited bright beams. So far such light sources are only available in the domain of a few Watts, restricting, e.g., the precision of quantum-limited metrology and the efficiency of coherent parametric processes. The phase space sketches to the right illustrate the different noise scaling for coherent input states. In coherent beam combining (left) the noise contributions from the independent inputs are progressively averaged out. The noise profile of the quantum-limited linear amplifier (right) is lower bounded by the 3dB limit (for high gain) which yields a significantly higher noise footprint.
References [1] T. Eidam et al., “Experimental observations of the threshold-like onset of mode instabilities in high power fiber amplifiers”, Opt. Express 19 (14), 13218-13224 (2011) [2] C. Gaida et al., “Coherent combination of two Tm-doped fiber amplifiers”, Opt. Lett. 40(10) 2301-2304 (2015) [3] C. M. Caves, “Quantum limits on noise in linear amplifiers”, Phys. Rev. D 26, 1817-1839 (1982)
44 Th11
Nanoscale non-invasive cross-sectional imaging with high-order harmonics
S. Fuchs, J. J. Abel, J. Nathanael, M. Wünsche, G. G. Paulus Friedrich Schiller University, Max-Wien-Platz 1, 07743 Jena, Germany Helmholtz Institute Jena, Fröbelstieg 3, 07743 Jena, Germany [email protected]
The average output power of the most advanced femtosecond lasers has increased beyond the 100-W level and may soon reach kilowatts. At the same time, ultrafast laser technology is maturing for the short- wave or even mid-IR spectral regions. Accordingly, high harmonics with flux previously only known from synchrotrons can be generated in the silicon transmission window and in the near future at even shorter wavelengths. Concerning imaging, high harmonics have two distinct advantages: First, they are almost perfectly coherent. This means that modern lensless imaging techniques like coherent diffraction imaging or ptychography can be applied, thus bypassing a central problem of XUV microscopy, namely the lack of lenses. First successes have been demonstrated by several groups in recent years and resolutions on the order of a few 10 nm have been achieved. Second, high harmonics inherit ultra-short duration from the lasers producing them or are even shorter due to spectral coherence. This implies the promise of ultrafast nanoscale imaging with a potential that has yet to be explored and exploited. A challenge for nanoscale XUV imaging with high harmonics is their broad bandwidth. In order to use coherent diffraction imaging or ptychography, the harmonic radiation needs to be monochromatized whereby a very substantial fraction of the total flux will be lost. Coherence tomography, in contrast, takes advantage of broadband light sources and enables non- invasive cross-sectional imaging. Recently, my group has demonstrated XUV coherence tomography (XCT) with high harmonics. An axial (depth) resolution of 20 nm and a sensitivity exceeding the one of transmission electron microscopes has been demonstrated. Lateral resolution, on the other hand, is limited by the numeric aperture.
References [1] S. Fuchs et al., Optical coherence tomography with nanoscale axial resolution using a laser-driven highharmonic source, Optica 4, 903 (2017) 350 nm 950μm 420μm
45 Th12
Photoionization probed via High Harmonic Generation Interferometry
Nirit Dudovich Department of Physics of Complex Systems, Weizmann Institute of Science, 76100 Rehovot, Israel [email protected]
Single-photon ionization is one of the most fundamental light matter interactions in nature, serving as a universal probe of the quantum state of matter. By probing the emitted electron, one can decode the full dynamics of the interaction. When photo-ionization is evolving in the presence of a strong laser field, the fundamental properties of the mechanism can be significantly altered. In the talk I will describe two approaches to probe the photoionization process. The first approach is based on XUV initiated high harmonic generation, combining the universality provided by single-photon ionization with the high resolution provided by the recollision self-probing mechanism. Such a measurement enables us to fully reconstruct the photoionization dynamics in the presence of the strong laser field. Our study reveals the rich, multiple quantum path nature of the underlying mechanism, demonstrating that it opens a new route in attosecond time-resolved spectroscopy. In the second approach we reveal the photoionization spectral phase by measuring the time-reversed process, photo-recombination. Using a state of the art XUV interferometer, perform an interferometric measurement between two XUV sources, allowing for their independent control with attosecond precision. We present a direct differential measurement of the partial wave phase shifts of helium and neon atoms, confirming the notion of scattering states, over a large spectral range. Our study bears the prospect of linear interferometric measurements of molecular orbitals as well as probing of electron correlations through resonances exposed to a strong-field environment.
46 Th13
Attosecond photoemission delay in molecules around giant resonances
Matthias Kling Physics Department, Ludwig-Maxmilians-Universität Munich, 85748 Garching, Germany; Max Planck Institute of Quantum Optics, 85748 Garching, Germany [email protected]
Ionization delays provide important information on the electronic structure of matter. Attosecond experiments have revealed that the photoionization of electrons occurs with measurable delays in atomic gases and solids [1]. For molecules, such experiments can shed light on many-particle correlations, and help to develop and validate theoretical models (see e.g. [2]). Only recently, Huppert et al. [3] have employed RABBITT (attosecond beating by interference of two- photon transitions) measurements to determine ionization delays in two molecules for a range of photon energies. They found delays up to 160 as for N2O caused by a shape resonance. In our work, we go beyond single electron excitations and focus on giant dipole/plasmon resonances. We have employed attosecond streaking to determine photoemission delays from ethyliodide molecules versus neon at photon energies around the giant I(4d) dipole resonance (see Fig. 1) near 100 eV. The collective electron dynamics have been predicted to result in negative photoionization delays in iodine and xenon [4], in sharp contrast to another recent theoretical study [5]. Our work aims to resolve this dispute. We compare the experimental results to predictions from quantum scattering theory and mixed quantum-classical simulations.
We also studied the photoemission delay in C60 near the giant plasmon resonance around 20 eV. Here, attosecond photoemission delays may provide insight into screening Figure 1 Streaking spectrograms recorded for and anti-screening of electrons in plasmonic fields [6]. To ethyliodide and neon at 80 eV photon energy. illuminate this aspect, we model the experimental results with mixed quantum-classical simulations.
References [1] L. Gallmann et al., “Photoemission and photoionization time delays and rates”, Struct. Dyn. 4, 061502 (2017). [2] P. Hockett et al., “Time delay in molecular photoionization”, J. Phys. B 49, 095602 (2016). [3] M. Huppert et al., “Attosecond Delays in Molecular Photoionization,” Phys. Rev. Lett. 117, 093001 (2016). [4] M. Magrakvelidze, H. Chakraborty, “Attosecond time delays in the valence photoionization of xenon and iodine at energies degenerate with core emissions”. J. Phys. Conf. Ser. 875, 022015 (2017). [5] L. Pi, A. Landsman, “Attosecond time delay in photoionization of noble-gas and halogen atoms”, Appl. Sci. 8, 322 (2018).
[6] T. Barillot et al., “Angular asymmetry and attosecond time delay from the giant plasmon resonance in C60 photonionization”, Phys. Rev. A 91, 033413 (2015).
47 Th21
Clocking electrons in strong-field ionization
Philip H. Bucksbaum, Adi Natan, James Cryan, Andrei Kamalov, Lucas Zipp PULSE Institute, SLAC National Acclerator Laboratory, Menlo Park, CA 94025 [email protected]
We have used phase-shaped strong laser fields to learn about the delays and advances that accompany strong-field ionization and recollision in atoms and molecules. This paper will concentrate on recent work, but also consider how the results inform problems from atomic tunnel ionization to future opportunities for vacuum tunnel ionization.
References [1] Zipp, L. J., et al. Optica 1, (2014): 361. doi:10.1364/OPTICA.1.000361 [2] Schumacher, D. W. et al, Physical Review A 54, (1996): 4271–4278. doi:10.1103/PhysRevA.54.4271
48 Th22
Laser-induced Coulomb explosion of molecules: Structure, dynamics, alignment
Henrik Stapelfeldt Aarhus University, Department of Chemistry, Langelandsgade 140, DK-8000 Aarhus C, Denmark [email protected]
I was introduced to femtosecond laser-induced Coulomb explosion during my post doc time in Paul Corkum’s research group in the mid-nineties. In collaboration with Eric Constant, a PhD student with Paul Corkum and Andre Bandrauk at that time, we applied Coulomb explosion to image dissociative vibrational wave packets in iodine molecules [1]. Since then I have used Coulomb explosion to explore structure, dynamics and alignment / orientation of many different molecules. In this talk I will describe some of these studies including fs time-resolved imaging of how a chiral molecules twists [2,3], identification of isomers of an aromatic molecule [4], characterization of how molecules – isolated as well as in a dissipative environment – are turned in space [5,6], and structure determination of weakly bonded molecular complexes inside helium nanodroplets [7].
References [1] H. Stapelfeldt et al., “Wave packet structure and dynamics measured by Coulomb explosion,” Phys. Rev. Lett. 74, 3780 (1995). [2] C. B. Madsen et al., “Manipulating the Torsion of Molecules by Strong Laser Pulses,” Phys. Rev. Lett. 102, 073007 (2009). [3] L. Christensen et al., “Dynamic Stark Control of Torsional Motion by a Pair of Laser Pulses,” Phys. Rev. Lett. 113, 073005 (2014). [4] M. Burt et al., “Communication: Gas-phase structural isomer identification by Coulomb explosion of aligned molecules,” J. Chem. Phys. 148, 091102 (2018). [5] L. Christensen et al., “Deconvoluting nonaxial recoil in Coulomb explosion measurements of molecular axis alignment,” Phys. Rev. A. 94, 023410 (2016). [6] B. Shepperson et al., “Strongly aligned molecules inside helium droplets in the near-adiabatic regime,” J. Chem. Phys. 147, 013946 (2017).
[7] J. D. Pickering et al., “Alignment and Imaging of the CS2 Dimer Inside Helium Nanodroplets,” Phys. Rev. Lett. 120, 113202 (2018).
49 Th23
Recollision-less High Harmonic Generation
Avner Fleischer1,2 and Oren Cohen2 1Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, 6997801 Israel and Tel-Aviv University center for Light-Matter-Interaction, Tel Aviv, 6997801 Israel 2Solid State Institute and Physics Department, Technion-Israel Institute of Technology, Haifa 32000, Israel
The phenomena of High Harmonic Generation (HHG) relies on the extreme-nonlinear optical phenomena of tunneling, and on electron recollision. Here we show theoretically how attosecond pulses of electrons and photons could be generated in the regime of linear optics. We utilize electron interference phenomena, initiated by an extreme ultra violet (XUV) laser field shined on atoms, in the presence of an infra-red (IR) laser field. As a result, attosecond electron pulses are generated, which are accompanied, as usual, by the emission of attosecond optical pulses, composed of high-order harmonics of the IR field. Both the electron and optical attosecond pulses are generated by the release of electrons, not by their recolliison. This recollision-less HHG process has a potential to bypass one of the biggest limitations accompanying the usual HHG scheme: low conversion efficiency due to the lateral spreading of the recolliding electronic wavepacket.
50 Th24
Electrons at the end of the tunnel
Sebastian Eckart1, Maksim Kunitski1, Martin Richter1, Alexander Hartung1, Jonas Rist1, Florian Trinter1, Kilian Fehre1, Nikolai Schlott1, Kevin Henrichs1, Lothar Ph. H. Schmidt1, Till Jahnke1, Markus Schöffler1, Kunlong Liu3, Ingo Barth3, Jivesh Kaushal2, Felipe Morales2, Misha Ivanov2, Olga Smirnova2, Reinhard Dörner1 1Institut für Kernphysik, Goethe-Universität Frankfurt am Main, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany. 2Max Born Institute, Max-Born-Str. 2A, 12489, Berlin, Germany. 3Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle (Saale), Germany. [email protected]
We will discuss new experiments on the momentum and the spin of the electron upon exit of the tunnel.
References [1] Trabert et. al. .Spin-and Angular Momentum in Strong-Field Ionization. Phys. Rev. Lett., 120 (2018) 043202 [2] Eckart et al. Making and detecting ring currents in a single atom by nonadiabatic tunneling in a strong laser field. Nature Physics (in print) [3] Hartung et al Electron spin polarization in strong-field ionization of Xenon atoms. Nature Photonics 10 (2016) 526
51 Th31
Virtual Detector Theory for Strong-Field Atomic Ionization
Xu Wang1, Justin Tian2 and J. H. Eberly2 1Graduate School, China Academy of Engineering Physics, Beijing 100193, China 2Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627, USA [email protected]
A virtual detector (VD) is an imaginary device located at a fixed position in space that extracts information from the wave packet passing through it. By recording the particle momentum and the corresponding probability current at each time, the VDs can accumulate and build the differential momentum distribution of the particle, in a way that resembles real experiments. In addition to being a tool for reducing the computational load, VDs have also been found useful in interpreting the ultrafast strong-field ionization process, especially the controversial quantum tunneling process. Normally differential momentum distributions are obtained by first integrating the wave function till the end of the laser pulse, then Fourier transforming it. A large numerical grid is thus needed to keep the wave function, which may spread to hundreds to thousands of atomic units in space driven by the strong laser field, making the computational load heavy. The original goal of the VD method, as proposed by Feuerstein and Thumm [1], was to provide an alternative and more economical way of calculating the momentum distributions (parallel attempts include a surface flux method [2] and an R-matrix method [3]). Later developments along this line include a hybrid quantum mechanical and classical trajectory approach by Wang et al. that takes full account of the long-range Coulomb potential [4]. A mathematical proof for the equivalence of the momentum distribution obtained from the VD method and from Fourier transformation has been given recently [5]. In addition to being a tool for reducing the computational load, the VD method was also found useful in helping to interpret and characterize the tunneling ionization process, which is known to be controversial. For example, Teeny et al. [6,7] and Ni et al. [8,9] use the VD method to extract tunneling-ionization- related information such as tunneling time, tunneling rate, position of tunneling exit, etc. Tian et al. [10] use it to solve an apparent controversy of electron longitudinal momentum at the tunneling exit [11-13]. Since quantum tunneling is the first step of the recollision picture, clear interpretation and precise characterization of the tunneling process is important.
References [1] B. Feuerstein and U. Thumm, “On the computation of momentum distributions within wavepacket propagation calculations”, JPB 36, 707 (2003). [2] L. Tao and A. Scrinzi, “Photo-electron momentum spectra from minimal volumes: the time-dependent surface flux method”, NJP 14, 013021 (2012). [3] L. Torlina and O. Smirnova, “Time-dependent analytical R-matrix approach for strong-field dynamics”, PRA 86, 043408 (2012). [4] X. Wang et al., “Extended virtual detector theory for strong-field atomic ionization”, PRL 110, 243001 (2013). [5] X. Wang et al., “Virtual detector theory for strong-field atomic ionization”, JPB accepted (2018). [6] N. Teeny et al., “Ionization time and exit momentum in strong-field tunnel ionization”, PRL 116, 063003 (2016). [7] N. Teeny et al., “Virtual-detector approach to tunnel ionization and tunneling times”, PRA 94, 022104 (2016). [8] H. Ni et al., “Tunneling ionization time resolved by backpropagation”, PRL 117, 023002 (2016). [9] H. Ni et al., “Tunneling exit characteristics from classical backpropagation of an ionized electron wave packet”, RPA 97, 013426 (2018). [10] J. Tian et al., “Numerical detector theory for the longitudinal momentum distribution of the electron in strong field ionization”, PRL 118, 213201 (2017). [11] A.N. Pfeiffer et al., “Probing the longitudinal momentum spread of the electron wave packet at the tunnel exit”, PRL 109, 083002 (2012). [12] C. Hofmann et al., “Comparison of different approaches to the longitudinal momentum spread after tunnel ionization”, JPB 46, 125601 (2012). [13] X. Sun et al., “Calibration of the initial longitudinal momentum spread of tunneling ionization”, PRA 89, 045402 (2014).
52 Th32
Controlling electron-electron correlation in frustrated double ionization of molecules with orthogonally polarized two-color laser fields
Agapi Emmanouilidou Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom [email protected]
We demonstrate the control of electron-electron correlation in frustrated double ionization (FDI) of the + two-electron triatomic molecule D3 when driven by two orthogonally polarized two-color laser fields. We employ a three-dimensional semi-classical model that fully accounts for the electron and nuclear motion in strong fields. We analyze the FDI probability and the distribution of the momentum of the escaping electron along the polarization direction of the longer wavelength and more intense laser field. These observables when considered in conjunction bear clear signatures of the prevalence or absence of electron-electron correlation in FDI, depending on the time-delay between the two laser pulses.
References [1] A. Cehn, M. Kling and A. Emmanouilidou, Phys. Rev. A 96, 033404 (2017).
53 Th33
The 3-step recollision process in laser driven solids
C. McDonald and T. Brabec Department of Physics, University of Ottawa [email protected]
The recent demonstration of HHG in solids has opened the door for an expansion of strong field physics from atomic and molecular gases to the condensed matter phase. HHG in semiconductors was found to be very similar to the 3-step process driving HHG in atomic gases. First, an electron hole pair is generated by ionization. Second, the electron is accelerated in the laser field. Third, upon recollision between electron and hole a harmonic photon is generated. In this talk, a range of topics related to HHG in solids will be discussed: the 3-step process of HHG in Bloch and in Wannier basis; 3-step process for HHG from impurities; what kind of structural information can be extracted from HHG in solids; and finally HHG in lower dimensional solids.
54 Th34
High-Harmonic Generation is the Sound of the 80s
Michael Spanner National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, Canada [email protected]
High-harmonic generation (HHG) is a nonlinear optical process where a wide plateau of harmonics are generated when intense laser fields interact with atoms, molecules, and solids (Fig.1a). The Yamaha DX7 was revolutionary electronic music synthesizer released in 1983 that quickly dominated the 80s pop music sound (Fig.1b). This contribution explores the overlap between the strong-field recollision physics leading to HHG and electronic music synthesis as implemented in the DX7.
a)
b)
Fig.1: Panel a) depicts typical characteristics of recollision-based high-harmonic generation (from Wikipedia). Panel b) shows the Yamaha DX7 music synthesizer (from Google Image Search).
55 Th41
Attosecond Probing of Core-Level Dynamics in Solids
Stephen R. Leone Departments of Chemistry and Physics and Lawrence Berkeley National Laboratory University of California, Berkeley, CA 94720 [email protected]
The seemingly simple act of the transfer of charge from one atom to another in a solid incorporates many of the fundamental problems facing attosecond scientists, including the need to develop a better understanding of the extremely fast processes of core-level screening and broadening, as well as electron rearrangements. In -Fe2O3, hematite, optical excitation initiates a transfer of an electron from an oxygen atom in the lattice to an Fe3+ ion, in a highly localized fashion, causing Fe3+ to become Fe2+. With attosecond transient absorption measurements [1], a nearly instantaneous broadening of the Fe3+ transition lineshape is observed, coincident with the optical excitation. However, the changes in overall electron configuration that cause the Fe3+ lineshape to decay and the Fe2+ lineshape to form are delayed by several femtoseconds. On a longer 100 fs timescale, the nuclei rearrange to isolate a small polaron in the lattice [2]. The implications of these short time dynamics will be considered. Metal dichalcogenide bulk materials exhibit remarkable new characteristics when subdivided to achieve single layers. Indirect gap materials become direct gap, optical excitons are more strongly bound, and screening properties significantly depend on the substrate for the single layer materials. Core-level excitons in the extreme ultraviolet, which would normally be difficult to observe because of relatively small shifts from the conduction band edge can also exhibit new properties in such single layer materials. In MoS2, a large red shift of approximately 4 eV is observed for the absorption edge of the Mo N2,3 transition at 32-35 eV in the extreme ultraviolet as the material is subdivided, compared to the bulk material, resulting in a narrow and strong absorption feature attributed to the observation of a core-level exciton. The lifetime of the core-level exciton is measured to be approximately 4 fs by attosecond transient absorption. Additionally, transient Stark shifts, electronic coherences, and population transfer are observed among the core-level states. The results provide a new probe for the electronic characterization of two-dimensional materials and core-level states.
References [1] M. Zürch, et al., “Direct and simultaneous observation of ultrafast electron and hole dynamics in germanium,” Nat. Comm. 8, 15734 (2017).
[2] L. M. Carneiro, et al., “Excitation wavelength dependent small polaron trapping of photoexcited carriers in -Fe2O3,” Nat. Mat. 16, 819 (2017).
56 Th42
Zepto-second Pump & Probe Experiments with Ion-Beam Methods
H. Schmidt-Böcking 1, A. Czasch 1, R. Dörner 1, S. Eckart 1, O. Jagutzki 1, R. Moshammer 2, M. Schöffler 1, L. Ph. Schmidt 1, R. Schuch 3, and J. Ullrich 4 1 Institut für Kernphysik, Universität Frankfurt, Frankfurt, Germany 2 Max-Planck Institut für Kernphysik, Heidelberg, Germany 3 FYSIKUM, Stockholm University, Alba Nova, 106 91 Stockholm, Sweden 4 Physikalisch Technische Bundesanstalt, Braunschweig, Germany [email protected]
So-called Pump & Probe measurements are today commonly identified with Two-pulse Laser Pump & Probe methods where the very short time delay Δt between the two pulses can be well adjusted by two different geometrical path ways yielding a time resolution in the atto-second range. But a kind of "Pump & Probe" measurements with time-delay determination have been performed already 100 years ago, e.g. by Stern and Volmer (1), when they measured the decay time of photon-excited J2 molecules using the thermal motion of the molecules as a fast clock. They obtained already 2 nano-second time resolution. Applying this method to fast ion beams ("beam foil technique" (2)) decay times could be measured with pico-second precision. By measuring the quantum beat structure in the spectra of quasi-molecular x-ray emission in fast ion-atom collisions Schuch et al. (3) have obtained for selected hydrogen-like heavy ion projectiles even a time resolution of about 10 zepto-seconds. Furthermore the method of "Pumping & Probing" should not be restricted to measurements where the time delay Δt is measureable. Even if Δt is not precisely measureable, one can measure in coincidence the momenta of many fragments (electrons and nuclei) emitted in the same reaction. These data provide also information on the entangled dynamics of these fragments. In multi-fragmentation processes commonly a cascade of Auger is emitted, where from the kinetic energies of these electrons the chronological sequence of the Auger electrons is known, one detects even multiple probing steps and has thus access to other fundamental aspects of many-particle dynamics in atomic physics (4). Intra-atomic and intra-molecular dynamics can take place even on the lower zepto-second level (10-20 second), i.e. about 5 orders of magnitude shorter than the presently available Laser pulses. In such a short time interval light travels only a distance of 0,03 Angström. To visualize this ultra-fast dynamics one needs clock-systems sensitive to ultra-fast time dependent processes. It may be a more philosophical issue whether such ultra-short time scales below one atto-second may be of any relevance in atomic physics. Such a time resolution allows the investigation of possible processes in molecules proceeding faster than speed of light, e.g whether the so-called collapse of a wave function is a non-local process instantaneously present everywhere in a molecule. Such ultra-short time delays can be measured and controlled by using projectiles (e.g. ions) moving with relativistic speed. Detecting interactions of the same ion at two different positions in an atom or a molecule (1. the “pump” position and 2. the “probe” position), from this relative distance and the velocity of the moving object the time delay between the two interactions can be deduced. Examples for ultra-short delay measurements are presented (3). E.G., if one bombards a hydrogen-like Cl16+ projectile ion on an Ar atom thus a 1sσ vacancy is already present on the incoming part of the collision and identical x rays can be emitted on the way into the collision (-t values) and on the way out of the collision (+t values). Since the transition amplitudes on the first half (way into the collision) interfere with those of the second half of the collision) like in a double slit experiment (see also Ramseys atomic-clock (5) separated-oscillating-field method) one can observe sub-atto-second characteristic quantum beat structures in the spectra of during the collision emitted x-rays (see figure 1). Figure 1: Measured x-ray spectra for the 2pπ-1sσ quasi- molecular transition in Cl 16+-Ar collisions (3). The x-rays are directly measured with a Si(Li)-detector in coincidence with scattered ions. The x-ray energy can be transferred into an inter- nuclear distance R via a correlation diagram. From the inter- nuclear distance R and the ion velocity the time scale can be calibrated.
References [1] O. Stern und M. Volmer, Über die Abklingungszeit der Fluoreszenz. Physik. Z., 20, 183-188 (1919); [2] H G Berry 1977 Rep. Prog. Phys. 40 155.; [3] R. Schuch et al., Quasimolecular X-Ray Spectroscopy for Slow Cl16+-Ar Collisions; Phys. Rev. A 37 (1988) 3313; [4] F. Trinter et al., Multi-fragment vector correlation imaging. A search for hidden dynamical symmetries in many-particle molecular; [5] N. F. Ramsey, A Molecular Beam Resonance Method with Separated Oscillating Fields, Phys. Rev. 78, 695 (1950)
57 Th43
Filament and Corona induced precipitation in a cloud chamber
Jingjing Ju1, Tie-Jun Wang1, Ruxin Li1, Shengzhe Du1, Haiyi Sun1, Yonghong Liu1, Ye Tian1, Yafeng Bai1, Yaoxiang Liu1, Na Chen1, Jingwei Wang1, Cheng Wang1, Jiansheng Liu1, Zhizhan Xu1 and S. L. Chin2 1Shanghai Institute of Optics and Fine Mechanics (SIOM), Shanghai, China. 2Centre d’Optique, Photonique et Laser (COPL), Université Laval, Québec, QC, Canada.
Both femtosecond laser filamentation and high voltage corona discharge could induce precipitation in a diffusion cloud chamber in which a temperature gradient was maintained. The principal mechanism seems to be the air motion induced by filamentation and corona discharge. Such air motion would mix up the moist air with a temperature gradient resulting in a super-saturation state. Precipitation would follow [1,2].
References [1] J. J. Ju et al, “Femtosecond laser filament induced condensation and precipitation in a cloud chamber”, Scientific Reports 6, 25417 (2016) [2] Jingjing Ju, Tie-Jun Wang, et al, “Corona discharge induced snow formation in a cloud chamber”, Scientific Report, 7, 11749 (2017).
58 Th44
The Life It Brings: Molecules in Laser Fields
Albert Stolow University of Ottawa and National Research Council Canada [email protected]
I began my scientific interactions with Paul Corkum nearly thirty years ago, in 1988. Over this period, Paul’s thoughts, intuition and historical perspective influenced my thinking in many ways. My innumerable discussions with Paul often reminded me of why I wanted to be a scientist in the first place: it simply was fun. Hence my title which borrows from a 1934 letter that Oppenheimer wrote to his younger brother, praising “physics and the obvious excellences of the life it brings”. In my talk, I will summarize progress and future directions for understanding polyatomic molecular dynamics in laser fields both weak and strong.
59 Fr11
On subtle difference between left and right: inducing and probing ultrafast chiral dynamics
Olga Smirnova Max Born Institute, Max Born Str 2A, 12489 Berlin Germany [email protected]
We describe a new technique of chiral recognition, based on the excitation of coherent helical motion of bound electrons in valence shells of a chiral molecule [1]. Unlike the helix of light, traditionally used for chiral recognition in neutral molecules, the helical motion of the electrons has the right size to explore molecular chirality, leading to strong ultrafast chiral response. The most established technique of probing chiral interactions, the photoabsorption circular dichroism, relies on interaction with circularly polarized light. Distinguishing right-handed from left-handed molecules relies on the molecule sensing the chiral nature of the circular light. The helix of the light-wave is given by its wavelength. Hence, for optical fields, it exceeds the size of a molecule by several orders of magnitude. As a consequence, the related chiral effect – the photoabsorption circular dichroism – is very small. Formally, to feel the pitch of the lightwave, one needs to look beyond the dipole approximation, relying on the magnetic component of the laser field. Small value of the chiral signal makes ultrafast measurements of chiral dynamics very challenging. One possible way of increasing chiral response is to avoid the reliance on magnetic field effects and therefore perform chiral measurements without chiral light. We describe the concept underlying such measurements. We present a unified description of several methods of chiral discrimination based on electric-dipole interactions. We show that, in spite of the fact that the physics underlying the appearance of chiral response is very different in all these methods, the chiral observable in all cases has a unique form. It is a polar vector given by the product of the molecular pseudoscalar and the field pseudovector. The latter is specified by configurations of the electromagnetic fields interacting with an isotropic ensemble of chiral molecules. The molecular pseudoscalar is a rotationally invariant property, which is composed from different molecule-specific vectors and, in the simplest case, is a triple product of such vectors. The key property that enables the chiral response is the non-coplanarity of the vectors forming such triple product. The key property that enables chiral detection without using chiral electromagnetic fields is the vectorial nature of the enantio-sensitive observable. Finally, we will discuss geometrical and topological origins of chiral response. Handedness is a purely geometrical degree of freedom. In analogy with solids, where geometry and topology play important role in electronic response, we show that one can introduce chiral fields and chiral charges of geometrical origin that drive one-photon chiral response and are somewhat reminiscent of Berry curvature and Chern number in solids.
References [1] S. Beaulieu, et al. “Photoexcitation Circular Dichroism in Chiral Molecules”, Nature Physics (2018) doi:10.1038/s41567-017-0038-z
60 Fr12
Passively Stable Coherent Combination of Ultrafast Fiber Lasers
Kevin F. Lee, M. E. Fermann 1IMRA America, Inc., 1044 Woodridge Ave., Ann Arbor, MI, 48105, USA [email protected]
Strong field physics relies on large and expensive Ti:sapphire lasers with multiple amplifiers and nonlinear conversion. Fiber lasers can directly produce femtosecond pulses in the near-infrared at high repetition rate, but with lower pulse energy. Thulium fiber lasers at 2 μm are already near the intensity needed for high harmonic generation in solids [1]. To bring fiber lasers into the strong-field regime, we present a method for scaling pulse energy, a new coherent combination interferometer design. We combine eight pulses while only needing one stabilize actuator, and with unidirectional propagation in the amplifiers. We call our interferometer design the DeReStacker. It takes each pulse, destacks it into many pulses, passes it to amplifiers, and then accepts the amplified pulses for restacking into a single strong pulse. The basic 2 pulse × 2 amplifier DeReStacker is shown in Figure 1 with retroreflectors drawn where the amplifiers would be. Each pulse icon represents a unit of pulse energy with a particular relative phase and timing. The π phase from reflection at the beam splitter when in air, and the choice of phase from adjusting the group delay of the two arms is used to force pulses that entered by the long path to leave by the short path and vice versa, resulting in the same total travel time for all pulses.
Figure 1. Schematic of the basic DeReStacker. Phases are chosen to force all pulses to take different paths when entering and leaving the DeReStacker, ensuring that they all leave at the same time.
We have successfully implemented a 4×2 pulse DeReStacker with nonlinear compression in two fiber amplifiers, combining eight 81 fs pulses for 351 mW average power and 122 MHz repetition rate. With further power scaling, fiber lasers will provide the compact sources needed for future applications of strong-field physics and high harmonic generation.
References [1] Kevin F. Lee et al., “Harmonic generation in solids with direct fiber laser pumping,” Opt. Lett. 42, 1113 (2017).
61 Fr13
Circular Polarization in Attosecond Phenomena and Applications
Andre D Bandrauk Laboratoire de Chimie Theorique,Universite de Sherbrooke, Sherbrooke,Que,J1K 2R1,Canada [email protected]
The imaging and ultimate control of electrons in matter requires laser pulse durations on a time scale associated with the atomic unit of time - 24 attoseconds (1 asec=10-18 s), the time for the 1s electron in the H atom to cross the Bohr radius, a0 = 0.0529 nm. Attosecond pulses at photon energies corresponding to the fundamental edge of matter, the soft XRay region above 200 eV permit the probing, imaging of electronic dynamics in matter. A soft XRay pulse duration of 43 asec has recently been achieved using intense linear polarization driving pulses[1].The main source of current linear polarization attosecond light pulses is high order harmonic generation, HHG in atoms and MHOHG in molecules. It is a highly nonlinear nonperturbative response of electrons in matter to ultrashort, femtosecond (1 fs = 10-15s) intense (I>1014 W/cm2) mid-IR laser pulses. The highly nonlinear radiative emission is modelled now as a recollision process after tunnel ionization in linear polarization, called the Corkum model, giving a cut- 2 2 off, ie, maximum photon energy at Ip+3.17Up[2], where Ip is the ionization potential, Up=E /4mw at maximum field amplitude E and frequency w. Recollision is suppressed with circularly polarized pulses whereas as shown as early as 1995 multiple frequency linear polarisation pulses [3] or a combination of co- or counter-rotating bichromatic circular polarization pulses with frequencies n1/n2 for integer n [4-5] induce recollision and copious harmonics of circular polarization [6-8] which are produced efficiently with counter rotating circular polarization pulses by recollision. The circular bichromatic pulse induced circular polarized HHG has been shown to be universal with a maximum intensity at photon energies Ip+2Up and also a maximum energy cut-off Ip+3.17Up but with Up calculated with the average frequency . Furthermore simulations based on molecular TDSE, s (Time-Dependent Schroedinger Equations) show that circularly polarised HHG and attosecond pulses are generated efficiently when the total counter-rotating bicircular electric field rotational symmetry Cn is the same as the symmetry of a target molecule [7-8]. The compatibility of net electric field and molecular symmetries allows also to create coherent electron currents, sources of intense attosecond magnetic field pulses [8-9].
References [1] T Gaumnitz et al., Opt Exp 25,27506(2017). [2] P B Corkum, Phys Rev Lett 71,1994(1993). [3] T Zuo, A D Bandrau, M Ivanov P B Corkum, Phys Rev A 51,3991(1995). [4] T Zuo, A D Bandrauk, J Nonl Opt Phys Mater 4,533(1995). [5] A D Bandrauk, H Z Lu, Phys Rev A 68,043408(2003). [6] S Long, W Becker, J K McIver, Phys Rev A 52,2262(1995). [7] A D Bandrauk, F Mauger, K J Yuan, J Phys B 49,23LT01(2016). [8] A D Bandrauk, J Guo, K J Yuan, J Opt 19,124016(2017). [9] K J Yuan, A D Bandrauk, Phys Rev A 88,013417(2013); 91,042509(2015); 92,063401(2015).
62 Fr21
High Energy Mid-Infrared Lasers by DC-OPA for Creating Intense Attosecond Light Bullets
Katsumi Midorikawa Riken Center for Advanced Photonics, 2-1 Hirosawa, Wako, Saitama 351-019, Japan [email protected]
In recent years, high-energy mid-infrared (MIR) femtosecond laser sources attract a lot of attentions owing to their potential applications for generating a tabletop ultrafast sub-keV to keV soft x-ray light, creating high-energy attosecond pulses, and investigating high-field laser physics. To obtain an intense MIR femtosecond laser pulses, optical parametric amplification (OPA) has been adopted widely. A standard ultrafast OPA which utilizes fs pump and seed can generate up to 10 mJ level pulses. Further energy scaling up is restricted by limited size and damage threshold of nonlinear crystals. To obtain TW-class MIR femtosecond laser pulses, a dual-chirped optical parametric amplification (DC-OPA) has been proposed theoretically [1] and demonstrated in experiment [2,3] by our group. In the DC-OPA scheme, a broadband laser of which pulse duration tunable from fs to 100 ps or longer is used as a pump for an OPA. An excellent energy scaling ability which is not restricted by crystal has been revealed. Also, DC-OPA can scale up energy without losing its spectrum bandwidth. Our strong MIR fs laser pulses produced by DC-OPA is extremely useful for creating intense attosecond light bullets with several promising advantages: 1) the reduced chirp of attosecond pulse is very helpful for creating short duration even without compensation; 2) the long driving wavelength is significantly helpful to extend photon energy of attosecond pulse to sub-keV region; 3) high energy of the MIR pulse is promising for energy scaling up (photon flux) of attosecond pulse even though the highly nonlinear generation process is intrinsically low efficiency. Our model simulation shows the high-order harmonic spectrum generated by high energy two channel MIR waveform synthesizer (1.95 μm + 1.4 μm) will produce a supercontinuum spectrum in “water window” region, which supports a 50 as attosecond pulse even without chirp compensation.
References [1] Q. Zhang et al., Opt. Express 19, 7190 (2011). [2] Y. Fu et al., Opt. Lett. 40, 5082 (2015). [3] Y. Fu et al., J. Opt. 17, 124001 (2015).
63 Fr22
Molecular frame angular distribution of tunnel ionization probability from molecular orbitals: HCl and ethanol cases
Hiroshi Akagi Kansai Photon Science Institute, National Institutes for Quantum and Radiological Science and Technology, Kizugawa, Kyoto 619-0215, Japan [email protected]
Strong field ionization of atoms/molecules in a linearly-polarized laser field can be followed by electron recollision [1], which induces high harmonic generation, non-sequential double ionization, etc. However, the ionization in a circularly-polarized laser field cannot lead to the following recollision process because the freed electron drifts away from the parent ion [2]. Instead, the electron gives us information of the initial tunneling direction, which reflects the structure of the molecular orbital (MO) the electron tunnels from. For dissociative ionization of molecules induced by circularly-polarized laser field, molecular frame photoelectron angular distribution (MFPAD) can be determined by measuring the tunneled electron and a fragment ion in coincidence. The ejected electron drifts in the direction perpendicular to the laser electric field direction at the moment of ionization [2,3]. The recoil direction of the fragment ion reflects the orientation of the parent molecule. We can derive MFPAD from the angle between their recoil vectors. By identifying a fragment ion, we possibly isolate the contribution of single MO from the total ionization events. In this presentation, I would like to present MFPADs derived for two molecules, HCl [4] and ethanol (CH3CD2OH) [5]. First, we discuss MFPADs derived for H+ and Cl+ ions produced from HCl molecule [4]. Bond softening of HCl allows us to select the tunnel ionization from the HOMO-1, one orbital below the highest occupied molecular orbital (HOMO), because HCl+ (X 2Π) ion produced by tunnel ionization from the HOMO is stable in an infrared laser field whereas the HCl+ (A 2Σ+) dissociates and produces the H+ or Cl+ ions through the bond-softening process. The observed MFPADs are almost identical, and are qualitatively similar to the structure of the HOMO-1. Thus, the MFPADs unambiguously identify the HOMO-1. Our results are the first identification of tunnel ionization from an orbital lower than HOMO. + + Then, we share with you MFPADs for CD2OH and CH3CD2 production channels of CH3CD2OH [5]. + The MFPAD for CD2OH channel shows preferential electron ejection in the direction of the CH3 side of + CH3CD2OH, whereas the MFPAD of the CH3CD2 channel is almost isotropic. The previous + measurement using He(I) suggested that CD2OH is produced from the first electronically excited state of + + + the parent CH3CD2OH ion, and CH3CD2 is produced from the second excited state of CH3CD2OH . + + Hence, the MFPADs of the CD2OH and CH3CD2 channels correspond to the electron ejection from HOMO-1 and HOMO-2, respectively.
References [1] P.B. Corkum, “Plasma Perspective on Strong-Field Multiphoton Ionization” Phys. Rev. Lett. 71, 1994 (1993). [2] P.B. Corkum et al., “Above-Threshold Ionization in the Long-Wavelength Limit” Phys. Rev. Lett. 62, 1259 (1989).
[3] A. Staudte et al., “Angular Tunneling Ionization Probability of Fixed-in-Space H2 Molecules in Intense Laser Pulses” Phys. Rev. Lett. 102 033004 (2009). [4] H. Akagi et al., “Laser Tunnel Ionization from Multiple Orbitals in HCl” Science 325, 1364 (2009). [5] H. Akagi et al., in preparation.
64 Fr23
Towards strong field science with longer wavelengths
Carlos Trallero-Herrero, Derrek Wilson, Adam Summers, Lianjie Xue, Stefan Zigo, Brandin Davis, Daniel Rolles, and Artem Rudenko Department of Physics, University of Connecticut, Storrs, CT James R. Macdonal Laboratory, and Department of Physics, Kansas State University, Manhattan, KS [email protected]
The scaling of strong field interactions with wavelength has been a topic in ultrafast physics for some time. In this talk I will cover the topic of electronic excitation in solids and its dependence with wavelength. In addition, I will mention recent optics developments on the generation of intense femtosecond pulses in the long wavelength infrared.
65 Fr24
Science of High Energy, Single-Cycled Laser
JONATHAN WHEELER DER-IZEST, Ecole Polytechnique, Route de Saclay, FR-91128, Palaiseau, France ELI-NP, Horia Hulubei - National Institute for Physics and Nuclear Engineering, 30 Reactorului Street, RO-077125, Bucharest-Magurele, Romania [email protected]
GÉRARD MOUROU DER-IZEST, Ecole Polytechnique, Route de Saclay, FR-91128, Palaiseau, France [email protected]
TOSHIKI TAJIMA Department of Physics and Astronomy, University of California, Irvine, 4164 Frederick Reines Hall, Irvine, California, USA ttajima@uci
With the advent of the Thin Film Compression [1-4], high energy single cycled laser pulses have become an eminent path to the new high field science future. An existing CPA high power laser pulse such as a commercially available PW laser may be readily converted into a single cycled laser pulse in the 10PW regime without losing much energy through the compression. We examine some of the scientific applications of this, such as the laser ion accelerator called SCLA [5] and bow wake electron acceleration. Further, such a single cycled laser pulse may be readily converted by the relativistic compression into a single cycled X-ray laser pulse [6]. We see that this is the quickest and very innovative way to ascend to the EW (Exawatt) and zs (zeptosecond) science and technology. We suggest that such X-ray laser pulses have a broad and new horizon of applications. We have begun exploring the X-ray crystal (or nanostructured) wakefield accelerator [8] and its broad and new applications into gamma rays. Here we make a brief sketch of our survey of this vista of the new developments.
References [1] Gérard Mourou, Gilles Cheriaux, Christophe Radier,Device for generating a short duration laser pulse US 20110299152 A1 [2] G. Mourou, S. Mironov, E. Khazanov, and A. Sergeev, “Single cycle thin film compressor opening the door to Zeptosecond-Exawatt physics,” Eur. Phys. [3] A. A. Voronin, A. M. Zheltikov, T. Ditmire, B. Rus, and G. Korn, “Subexawatt few-cycle lightwave generation via multipetawatt pulse compression,” Opt. Commun. 291, 299–303 (2013). [4] P. Lassonde, S. Mironov, S. Fourmaux, S. Payeur, E. Khazanov, A. Sergeev, J.-C. Kieffer, and G. Mourou, “High energy femtosecond pulse compression,” Laser Phys. Lett. 13, 75401 (2016). [5] M. L. Zhou, X. Q. Yan, G. Mourou, J. A. Wheeler, J. H. Bin, J. Schreiber, and T. Tajima, “Proton acceleration by single-cycle laser pulses offers a novel monoenergetic and stable operating regime,” Phys. Plasmas 23, 43112 (2016) [6] N. M. Naumova, J. A. Nees, I. V. Sokolov, B. Hou, and G. A. Mourou, “Relativistic Generation of Isolated Attosecond Pulses in a λ^{3} Focal Volume,” Phys. Rev. Lett. 92, 3–6 (2004). [7] T. Tajima, “Laser acceleration in novel media,” Eur. Phys. J. Spec. Top. 223, 1037–1044 (2014). [8] X. Zhang, T. Tajima, D. Farinella, Y. Shin, G. Mourou, J. Wheeler, P. Taborek, P. Chen, F. Dollar, and B. Shen, “Particle-in-cell simulation of x-ray wakefield acceleration and betatron radiation in nanotubes,” Phys. Rev. Accel. Beams 19, 101004 (2016)
66 Fr31
Strong field spectroscopy of electron dynamics: from laser filaments to strongly correlated solids
Misha Ivanov Max Born Institute, Max Born Str 2A, 12489 Berlin Germany [email protected]
Interaction of intense infrared laser light with matter, be it gases or solids, leads to rich and highly nonlinear electron dynamics. This talk will cover two very different examples. The first deals with gases, the second with strongly correlated solids. In atoms, unusual states can be created by light fields with strengths comparable to the Coulomb field that binds valence electrons in atoms. One would expect that such fields would easily set a valence electron free, perhaps within a single laser cycle. Yet, since late 1980s, theorists have speculated that atomic states become more stable when the strength of the laser field substantially exceeds the Coulomb attraction to the ionic core. The electron becomes nearly but not completely free: rapidly oscillating in the laser field, it still feels residual attraction to the core, which keeps it bound. I will describe a combination of experimental and theoretical results which show that these states arise not only in isolated atoms, but also in gases at and above atmospheric pressure, where they can act as a gain medium during laser filamentation. Using properly shaped laser pulses, gain in these states can be achieved within just a few cycles of the guided field, leading to amplified emission in the visible, at lines peculiar to the laser-dressed atom. Our work suggests that these unusual states of neutral atoms can be exploited to create a general ultrafast gain mechanism during laser filamentation. The second brings together two topics that, until very recently, have been the focus of intense but non- overlapping research efforts. The first concerns high harmonic generation in solids, which occurs when intense light field excites highly non-equilibrium electronic response in a semiconductor or a dielectric. The second concerns many-body dynamics in strongly correlated systems such as the Mott insulator. Using theorist’s model of a strongly correlated solid: the Hubbard model, we show that high harmonic generation can be used to time-resolve ultrafast many-body dynamics associated with optically driven phase transition, with accuracy far exceeding one cycle of the driving light field. These results pave the way for time-resolving highly non-equilibrium many body dynamics in strongly correlated systems, with few femtosecond accuracy.
67 Fr32
From Black Holes to Black Mold
Marlan Scully IQSE, Texas A&M University, College Station, TX, 77840, USA Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544, USA [email protected] 1. Radiation from Atoms Falling into a Black Hole [1] We show that atoms falling from outside through a cavity into a black hole (BH) emit acceleration radiation which to a distant observer looks much like Hawking BH radiation. In particular, we find the entropy of the acceleration radiation via a simple laser-like analysis.
2. Two-Photon Infrared Resonance Can Enhance Coherent Raman Scattering [2] We present a new technique for attaining efficient low- background coherent Raman scattering where Raman coherence is mediated by a tunable infrared laser in two-photon resonance with a vibrational transition.
References [1] M.O. Scully, S. Fulling, D. Lee, D. Page, W. Schleich, A. Sokolov, A. Svidzinsky, Opt. & Phot. News 29, 34 (2018). [2] A. Traverso, B. Hokr, Z. Yi, L. Yuan, S. Yamaguchi, M.O. Scully, V. Yakovlev, Phys. Rev. Lett. 120, 063602 (2018).
68 Fr33
Next-generation attosecond metrology
Ferenc Krausz Max-Planck-Institute of Quantum Optics Hans-Kopfermann-Strasse 1, 85748 Garching, Germany and Ludwig-Maximilians-Universität München Am Coulombwall 1, 85748 Garching, Germany [email protected]
Born around the turn of the new millennium, attosecond metrology has permitted the observation of atomic-scale electron dynamics in real time. Until recently, this capability has relied on attosecond extreme ultraviolet pulses, generated and measured in complex vacuum systems. Attosecond metrology 2.0 is now about to change this state of matters profoundly. Sub-femtosecond current injection into wide- gap materials can directly probe ultrafast electron phenomena in condensed matter systems and also be used for sampling the electric field of light up to ultraviolet frequencies. Petahertz field sampling draws on a robust solid-state circuitry and routine few-cycle laser technology, opening the door for complete characterization of classical fields all the way from the far infrared to the vacuum ultraviolet. These fields, with accurately measured temporal evolution, serve as unique probe for the dynamic (polarization) response of matter. Field-resolved spectroscopy will access (valence) electronic as well as nuclear motions in all forms of matter and constitutes a generalization of pump-probe approaches. Its implementation with a solid-state instrumentation opens the door for real-world applications, such as early cancer detection by measuring miniscule changes of the molecular composition of blood (liquid biopsy) via field-resolved vibrational molecular fingerprinting. About the author Ferenc Krausz (*1962 in Mór/Hungary) earned his degree in Electrical Engineering at the Technical University Budapest (1985). He completed his doctorate in Laser Physics at the Technische Universität (TU) Vienna (1991) where he habilitated in the same research field in 1993, took up assistant professorship in 1998 and full professorship in 1999. In 2003, Ferenc Krausz was appointed Director of the Max-Planck-Institute of Quantum Optics (MPQ) in Garching. In October 2004, he became professor at the Faculty of Physics of Ludwig-Maximilians- Universität (LMU) Munich and since then holds the Chair of Experimental Physics – Laser Physics. In a series of experiments performed between 2001 and 2004, Ferenc Krausz and his team succeeded in producing, measuring and using attosecond light pulses for tracing atomic-scale electronic motions. Since then, Ferenc Krausz is considered to be – together with Paul Corkum - founder of the field of Attosecond Physics, a field devoted to real-time observation and control of electron phenomena, as also acknowledged by their selection as 2015 Thomson Reuters Citation Laureates.
69 Fr34
Looking forward after 25 years of re-collision
Paul B. Corkum Joint Attosecond Science Laboratory, National Research Council and University of Ottawa 100 Sussex Drive, Ottawa ON K1A 0R6 Canada [email protected]
The idea of re-collision was transferred to atomic physics from plasma physics where electron-ion collisions are of critical importance. In my work, re-collision appeared in 1988-89 when we considered the lateral expansion of the electron wavefunction by connecting Reiss’s model of ATI with a semi- classical model. Stimulated by a set of experiments and calculations published between 1989 and 1992, it took another four years to integrate re-collision into a more complete model of extreme nonlinear optics. This new model rapidly led to new concepts such as attosecond pulse generation, the attosecond streaking and self-imaging. Recently, experiments are again forcing us to extend the horizon of extreme nonlinear optics. In solids, as in gases, it appears that, following their creation, electron-hole dynamics leads to high harmonics. Re- collision seems responsible in silicon, the most important semiconductors. But new experiments hint even broader applications of extreme nonlinear optics. For example, graphene and other mono-layered materials confirm that only a single atomic layer is required for a measurable signal. This suggests that it will be possible to use extreme nonlinear optics to study surface chemistry. In addition, in some cases, large molecules are not so different than solids and so, perhaps, extreme nonlinear optics may offer insight into their structure and chemistry – with carbon nanotubes already under study. There are still other exciting new frontiers to be explored and it is not impossible that, 25 years from now, re-collision will have permeated fields of science beyond physics.
70
ABSTRACTS – POSTERS Tuesday, May 8, 2018
Tuesday
All-optical interferometric probing of attosecond electronic wavepackets
Doron Azoury, Michael Krüger, Omer Kneller, Baptiste Febre, Bernard Pons, Yann Mairesse, Nirit Dudovich Department of Physics of Complex Systems, Weizmann Institute of Science, 234 Herzl St., 76100 Rehovot, Israel Université de Bordeaux – CNRS – CEA, CELIA, UMR5107, F33405 Talence, France [email protected]
Photoelectron spectroscopy is a powerful method that provides insight into the electronic structure of a wide range of systems. Interferometric studies of photoelectrons are now able to access the spectroscopic information encoded in the electronic wavefunction and reveal attosecond time delays as the electrons emerge from atoms or molecules [1,2]. The time-reversed process of photo-ionization – photo- recombination – encodes identical information, yet extracting it requires an interferometric measurement. Here we demonstrate all-optical XUV interferometry of two independent phase-locked attosecond pulse trains, encoding two recombination events with a temporal resolution of about 5as. By performing differential measurements, we gain a direct access to the absolute phase shifts between two different electronic wavefunctions associated with neon and helium atoms over a large energy range. In particular, our results provide a direct measurement of the species-resolved partial wave phase shift of the electronic wavefunction in the continuum. In the next step, we applied our scheme to probe the argon atom, where we demonstrated a direct measurement of its complex dipole phase. The strong-field induced spatial confinement allowed us to follow the rapid variation of the dipole phase over the energy range of the Cooper minimum, visualizing the functionality of the angular momentum propensity rule in the vicinity of an atomic structure. Our study bears the prospect of linear interferometric measurements for probing molecular orbitals as well as probing of electron correlations through resonances exposed to a strong-field environment.
References [1] K. Klünder, “Probing Single-Photon Ionization on the Attosecond Time Scale”, Phys. Rev. Lett. 106, 143002 (2011). [2] D. Villeneuve, “Coherent imaging of an attosecond electron wave packet”, Science 356 (6343), 1150 (2017).
72 Tuesday
Attosecond-Resolved Photoionization of Chiral Molecules
S. Beaulieu1,2, A. Comby1, A. Clergerie1, J. Caillat3, D. Descamps1, N. Dudovich4, B. Fabre1, R. Géneaux5, F. Légaré2, S. Petit1, B. Pons1, G. Porat4, T. Ruchon5, R. Taı̈ eb3, V. Blanchet1 & Y. Mairesse1 1Université de Bordeaux - CNRS - CEA, CELIA, UMR5107, F33405 Talence, France, 2Institut Natinal de la Recherche Scientifique, Varennes, Quebec, Canada, 3Université Paris-Sorbonne, UPMC Université Paris VI, UMR 7614, LCPMR, Paris, France 4Department of Physics of Complex Systems, Weizmann Institute of Science, 76100, Rehovot, Israel 5LIDYL, CEA, CNRS, Université Paris-Saclay, CEA Saclay 91191 Gif-sur-Yvette, France [email protected]
Bolts and nuts are amongst the most common chiral objects in our macroscopic world. Their chiral nature is used to convert rotation to directional translation: rotating the nut on a bolt induces its translation forward or backward, depending on the rotation direction. A very similar effect occurs in the microscopic world when enantiopure chiral molecules are photoionized by circularly polarized radiation. The ejected photoelectrons tend to go forward or backward relative to the light propagation axis, depending on the helicity of the ionizing light and the handedness of the molecules. As a result, the photoelectron angular distribution shows an asymmetry, called photoelectron circular dichroism (PECD). This asymmetry is one of the most sensitive probes of static and dynamical molecular chirality. It originates from subtle modifications of the outgoing electron scattering in the chiral molecular potential. PECD emerges in all ionization regimes: in single photon, multiphoton, above threshold and tunneling ionization. In this talk, we will focus on the use of attosecond (as) photoelectron interferometry to capture the ultrafast dynamics of chiral photoionization. Using this technique, we have measured the angularly- resolved photoionization dynamics with a precision on the order of few-attoseconds. For non-resonant photoionization, we measured delays of sub-20 as between electrons emitted forward and backward. These delays change sign upon switching the enantiomer or helicity of the electric field. Moreover, we have measured the photoelectron wavepacket spectral amplitude and phase around a near-threshold autoionizing resonance. This allows reconstructing the angularly-resolved temporal profile of the resonant photoelectron wavepacket. It shows complex temporal structures, reflecting the interference between direct and indirect ionization pathways. This temporal structure presents strong forward/backward asymmetry, revealing the chiral character of the autoionizing process [8]. In conclusion, our results show that using circularly polarized photons to drive photoionization of chiral molecules induces asymmetric delays in the photoemission, on both femtosecond and attosecond timescales.
References [1] Beaulieu et al. , “Attosecond-resolved photoionization of chiral molecules” Science 358, 1288-1294 (2017).
73 Tuesday
Phase- and Intensity-Resolved Measurements of Above Threshold Ionization by Few-Cycle Pulses
Matthias Kübel1, Mathias Arbeiter2, Thomas Fennel2, Matthias F. Kling1,3, Boris Bergues1,3 1Ludwig-Maximilians-Universität München, Am Coulombwall 1, Garching, Germany 2Institute of Physics, University of Rostock, Universitätsplatz 3, D-18051 Rostock, Germany 3Max-Planck-Institut für Quantenoptik, Hans-Kopfermannstr.1, D-85748 Garching, Germany [email protected]
We study the combined intensity and carrier-envelope phase (CEP)-dependence of the longitudinal momentum distribution of photoelectrons produced via above-threshold ionization of argon by a few- cycle laser pulse with a center wavelength of 750 nm. Our measurements are carried out using a systematic intensity and CEP scanning method. We observe a prominent maximum in the CEP-dependent left-right asymmetry at photoelectron energies of twice the ponderomotive potential (UP), which is persistent over the entire intensity range of our study [1].
Fig. 1. Position of the asymmetry maximum, Em, versus intensity. The experimental data, which were obtained in two separate experiments with different focal conditions, are compared to results obtained from the numerical solution of the three- dimensional time-dependent Schrödinger equation (TDSE). The TDSE results were averaged over different focal geometries. The inset shows the measured and calculated intensity dependence of Em in units of the ponderomotive potential UP.
Fig. 1 shows that the position of the asymmetry maximum, Em, agrees with 2UP within a 10% margin. The robustness of Em allows for a simple, reliable and accurate determination of the laser intensity on target, when CEP-stable or CEP-tagged few-cycle pulses are used.
In addition to the 2 Up maximum we observe further asymmetry maxima at 0.3Up and 0.8Up whose positions (in multiples of Up) are also intensity independent. Based on TDSE and semi-classical simulations we attribute these maxima to intra-cycle interferences [2,3]. We discuss how our method could be used to benchmark model potentials for complex atoms.
References [1] M. Kübel, Mathias Arbeiter, et al., (submitted to J. Phys. B special issue). [2] G. F. Gribakin and M. Yu. Kuchiev, “Multiphoton detachment of electrons from negative ions,” Phys. Rev. A, 55(5), 3760 (1997). [3] B. Bergues, Z. Ansari, et al., “Photodetachment in a strong laser field: An experimental test of Keldysh-like theories,” Phys. Rev. A, 75(6) 063415 (2007).
74 Tuesday
Probing the Phase Transition in VO2 Using Few-Cycle 1.8 μm Pulses
M.R. Bionta1,*, V. Wanie1, V. Gruson1,2, J. Chaillou1, N. Émond1, D. Lepage1, P. Lassonde1, M. Chaker1, and F. Légaré1 1Centre Énergie Matériaux et Télécommunications, Institut National de la Recherche Scientifique, 1650 Boulevard Lionel-Boulet, Varennes, Quebec, Canada J3X 1S2 2Department of Physics, The Ohio State University, 191 West Woodruff Avenue, Columbus, Ohio 43210, USA [email protected]
We observe a nearly instantaneous triggering of the phase transition in VO2 using transient, time-resolved absorption techniques from few-cycle, infrared (1.8 μm) laser pulses. The results are in agreement with the Mott-Hubbard insulator model, characterized by electronic holon-doublon pair creation that initiates the insulator-to-metal phase transition within the material. The spectral resolution provided by this technique can be exploited to measure the chirp of the probe pulses. Effects from probing above and below the band gap of the material are also discussed.
References [1] M.R. Bionta et al., Phys. Rev. B, 97, 125126 (2018).
75 Tuesday
Extreme focusing by axisymmetric systems: The inverse problem
Jeck Borne1, Denis Panneton1,2, Michel Piché1, and Simon Thibault1 1 Centre d'optique, photonique et laser, Université Laval, Quebec City, Quebec G1V 0A6, Canada 2 INO, Quebec City, Quebec G1P 4S4, Canada [email protected]
The precise knowledge of electromagnetic field distributions under conditions of extreme focusing is useful for various applications. Exploiting the characteristics of nonparaxial focusing systems has proven to be crucial to enhance optical performances in many areas [1,2]. Therefore, the development of an efficient inversion method where the ideal field distribution at focus defines the beam incident on the focusing system is of interest. Using the Richards-Wolf nonparaxial formalism [3], schemes addressing the inverse problem have been reported [4]. In this presentation, we revisit analytic inversion methods involving radially-polarized beams focused by axisymmetric nonparaxial systems without any restriction on the nature of the system or the field distribution. Our approach is based on mathematical considerations exploiting known transforms. We have fixed a criterion to conclude on the validity of the plane wave spectrum of the obtained incident illumination. Numerical implementation of the method leads to results in good agreement with the targeted fields. We are able to extend the proposed method to treat the inversion of transverse field distributions for other polarization states.
Figure 1. Results from the inversion method aiming to produce a longitudinally-polarized field with a radial profile Ez (0, r) = sinc(2πr/λ) at the focus of a parabolic mirror. In (a), the gray dotted lines indicate the limits of the plane wave spectrum required to obtain the targeted field distribution (in units of 1/ λ). In b) the computed illumination pattern is shown to cover the full domain of incidence angles on the parabola (from 0 to π). In c) and d), we show that the computed field has essentially the profile of the targeted field distribution and, in e), the profile of associated radial field component is presented.
References [1] X. Li, P. Venugopalan, H. Ren, M. Hong, and M. Gu, “Super-resolved pure-transverse focal fields with an enhanced energy density through focus of an azimuthally polarized first-order vortex beam,” Optics Letters 39, 5961 (2014). [2] Q. Zhan, “Trapping metallic Rayleigh particles with radial polarization,” Optics Express 12, 3377–3382 (2004). [3] B. Richards and E. Wolf, “Electromagnetic diffraction in optical systems. ii. structure of the image field in an aplanatic system,” Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences (1934-1990) 253, 358–379 (1959). [4] J. Hao, Z. Yu, H. Chen, Z. Chen, H.-T. Wang, and J. Ding, “Light field shaping by tailoring both phase and polarization.” Applied Optics 53, 785 (2014).
76 Tuesday
Ionization Dynamics in Ultrafast Strong Field Ionization of C60 Graham G. Brown1,2, V.R. Bhardwaj1, P. B. Corkum1,2 1Department of Physics, University of Ottawa, 25 Templeton Street, Ottawa, Ontario, Canada K1N 6N5 2National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, K1N 5A2 [email protected]
Blurring the distinction between solid-state physics and molecular physics, C60 is an ideal system for the study of multi-electron dynamics using ultrashort laser pulses. The generation of highly charged ions of C60 using infrared pulses has been reported and this has been demonstrated to be more efficient with shorter pulse durations [1]. An inherent limit, however, arises as the pulse duration decreases. As pulse durations approach single-cycle timescales, electrons which are accelerated away from the ion after tunnel ionization repel the remaining bound electrons, suppressing further ionization. Here, we report an experiment which measured the ionization yield from C60 for four pulse durations, ranging from few- cycle (12 fs FWHM) to many-cycle (79 fs FWHM) pulse durations, over a broad range of intensities. The experimental setup consisted of an infrared beam of wavelength 1.8 µm generated by an optical parametric amplifier pumped with a Ti:Sapphire laser, passed through a hollow-core fibre filled with Argon gas. The maximum pulse energy used in the experiment was 490 µJ. These pulses were focused into an ion time-of-flight mass spectrometer, in which a C60 vapor was generated using a resistive-heating oven at a temperature of 500 K. The peak intensity of the pulses was scaled using a polarizing filter and half-wave plate. The ionization rates for higher charge states relative to the rate of single and double ionization was observed to decrease for shorter pulse durations. Theoretical calculations to supplement the experiment were done using a real-time and real-space time- dependent density functional theory (TD-DFT) [2] which treats the C60 molecule as a jellium shell with azimuthal symmetry using the Lanczos time-propagation algorithm [3]. Calculations for various pulse durations were done and these calculations elucidate two features present for C60: (i) as the pulse duration increases, there is a suppression of ionization for higher charge states which is attributable to the Coulomb repulsion between freed and bound electrons; (ii) after tunneling into the continuum, the wave- packet diffusion of the ionized electrons is rapid when compared with that of an atom of similar ionization potential. This rapid diffusion can be attributed to the geometry of the molecule and the large angular momenta of the valence electrons. These two effects also explain the significantly broader ellipticity dependence of recollision in C60 observed in [4]. Additionally, the response of the excitation of the giant surface plasmon [5] resonance with an attosecond pulse and a subsequent infrared pulse was investigated with the TD-DFT model. A significant increase in ionization yield due to an infrared pulse is observed after excitation of the surface plasmon resonance.
References [1] Wong, M. (2014). High-Harmonic Spectroscopy of Complex Molecules (Doctoral dissertation). Retrieved from https://ruor.uottawa.ca [2] Andrade X. Real-Space Density Functional Theory on Graphical Processing Units: Computational Approach and Comparison to Gaussian Basis Set Methods. J. Chem. Theory Comput. 2013, 9(10), 4360−4373 [3] Frapiccini, A, et al. Explicit schemes for time propagating many-body wave functions. Phys. Rev. A 89, 023418 (2014) [4] V.R. Bhardwaj, et al. Phys. Rev. Lett. 91, 203004
[5] Scully, S. W. J. Photoexcitation of a Volume Plasmon in C60 Ions. Phys. Rev. Lett. 94, 065503
77 Tuesday
Designing Chirped Pulse Amplifiers on the Perspective of Time Lens Imaging
Xuanchao Qin, Shaozhen Liu, Yu Chen, Le Huang, Tao Cao, Ziyue Guo, Kailin Hu, Jikun Yan and Jiahui Peng* School of Optical and Electronic Information, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, China, 430047 *[email protected]
The chirped pulse amplifier (CPA) has been widely used for amplifying ultrashort optical pulses in high- power femtosecond laser systems [1,2]. To design a CPA, phase shifts caused by dispersion and self- phase modulation (SPM) as well as the gain saturation effect should be considered simultaneously, making a straightforward calculation intricate. Here, we show that the time lens imaging theory can help to simplify the process of designing a CPA. A time lens imaging system usually consists of a delay line introducing a group delay dispersion (GDD) 2 of D1, an element (time lens) introducing a quadratic temporal phase of exp(iτ / 2Df), and another delay line introducing a GDD of D2. Analogous to the spatial lens imaging, if the imaging condition 1/D1 + 1/D2 = 1/Df is satisfied, the output pulse will keep the same shape as the input with a pulse width magnification of |M| = |D2 / D1| [3]. Obviously, most CPAs can be viewed as a special temporal imaging system, where the stretcher, the gain medium and the compressor can be characterized by D1, Df, and D2, respectively. If a CPA is designed according to the imaging condition 1/D1 + 1/D2 = 1/Df, the output pulse will keep undistorted and its duration can be easily estimated. Moreover, short pulse durations can be obtained with a reasonably small magnification (|M|) by such a time lens. We have designed a fibre-based CPA satisfying the temporal imaging condition, and the measured output pulse duration agreed well with the value predicted by |M|, which conformed that a CPA can be really treated as a time lens imaging system. Besides, it was usually thought that the time lens approximation 2 was true only when D1 >> τ0 [3], where τ0 is the input pulse duration. However, our experiments 2 confirmed that the CPA could still be viewed as a time lens imaging system even when D1 = 1.6τ0 . Furthermore, we also tried to optimize the stretching fibre length to obtain the shortest pulse duration. The best length was found to be very close to the designed length. It was not surprising because our calculations had confirmed that the output pulse was nearly transformed-limited if the time lens approximation was valid.
References [1] D. Strickland and G. Mourou, “Compression of amplified chirped optical pulses”, Optics Communications 56(3), 219-221 (1985). [2] C. Rolland and P. B. Corkum, “Compression of high-power optical pulses”, JOSA B 5(3), 641-647 (1988). [3] B. Kolner, “Space-time duality and the theory of temporal imaging”, IEEE Journal of Quantum Electronics 30(8), 1951-1963 (1994).
78 Tuesday
Self-guided HHG for single-shot spectroscopy in the water window
V. Cardin1, B. E. Schimdt1,2, N. Thiré1,3, S. Beaulieu1,4, V. Wanie1,5, M. Negro5, C. Vozzi5, 6 1 V. Tosa , and F. Légaré 1 INRS– Énergie, Matériaux, Télécommunications, Varennes, Qc. Canada J3X1P7 2 few-cycle Inc., Montreal, Qc. Canada H1L5W5 3 Fastlite, 06560 Valbonne, Sophia Antipolis, France 4 Université de Bordeaux - CNRS - CEA, CELIA, UMR5107, F33405 Talence, France 5 Institute for Photonics and Nanotechnologies CNR-IFN, 20133 Milano, Italy 6 National Institute for R&D Isotopic and Molecular Technologies, 400293 Cluj-Napoca, Romania [email protected]
Due to its high technological potential in bioimaging [1], optimizing HHG yield for photons with energy in the water window is a topic of extensive research. Here, we demonstrate that self-guided propagation of high energy infrared pulses [2] in a high-pressure gas cell provide ideal conditions to achieve a bright, collimated x-ray beam with a cut-off energy closing the water window.
Figure 1 : Water window harmonic spectra and beam profile. Shown are the different absorption edges of metallic and polymer foils. The beam profile shows a 3.0mm FWHM, corresponding to a 2mrad divergence (full angle).
The spectra presented in figure 1 show the carbon K-edge and titanium L2,3-edge. We measured a flux of 1.0x105 photons/shot in the entire water window. The total energy in the harmonic pulse is calculated to be 16 pJ, i.e. a conversion efficiency of 2.1x10-9. This efficiency is comparable to HHG in a capillary [3]. A systematic study of the parameters critical for efficient HHG leads us to the conclusion that intensity clamping is occurring in the gas cell due to an ionization steady state. 3D wave equations confirmed the creation of this channel. The simulations reproduce a number of observed features, e.g. the optimal cell to geometrical focus distance (4 mm), the fixed cut-off with increasing helium pressure or cell length and the maximum clamped intensity limiting the HHG cut-off near the oxygen K-edge.
References: [1] J-F Adam, J-P Moy et al. “Table-top water window transmission x-ray microscopy: Review of the key issues, and conceptual design of an instrument for biology.” Rev. Sci. Instrum. 76 91301 (2005) [2] N. Thiré, S. Beaulieu et al. “10 mJ 5-cycle pulses at 1.8 μm through optical parametric amplification.” Appl. Phys. Lett. 106, 91110 (2015). [3] M. C. Chen, P. Arpin et al. « Bright, coherent, ultrafast soft x-ray harmonics spanning the water window from a tabletop light source.” Phys. Rev. Lett. 105, 173901 (2010).
79 Tuesday
Temporal Characterization of Multi-cycle Laser Pulses using the Tunneling Ionization Method
Wosik Cho1,2, Seung Beam Park1, Sung In Hwang1, and Kyung Taec Kim1,2* 1Center for Relativistic Laser Science, Institute for Basic Science (IBS), Gwangju 61005, Korea 2Department of Physics and Photon Science, Gwangju Institute of Science and Technology (GIST), Gwangju 61005,Korea *[email protected]
The development of ultrashort laser technology has enabled ultrafast phenomena to be studied with an unprecedented temporal resolution. The temporal characterization of ultrashort laser pulses is particularly important to understand the ultrafast light-matter interactions. There are many techniques in which the response of a nonlinear medium is utilized. These are techniques known as FROG [1], SPIDER [2] and D-scan [3]. They can be conveniently applied in many applications [4], but the applicable bandwidth is limited due to the phase matching and damage issues. There are other approaches in which an ultrafast temporal gate such as an attosecond XUV pulse [5] or an electron trajectory in the process of high harmonic generation [6], [7] is utilized. Although these techniques completely measure the electric field of the laser pulse, they require complicated x-ray generation and detection equipment. Recently, a new temporal characterization called tunneling ionization with a perturbation for the time-domain observation of electric-field (TIPTOE) has been introduced [8]. The TIPTOE method utilizes the extreme nonlinearity of ionization of air molecules. Here, we demonstrate that the TIPTOE method can be applied for multi- cycle laser pulses. The numerical calculations obtained by using the ADK ionization model and by solving the time-dependent Schrodinger equation are discussed. The experimental results obtained using the TIPTOE and FROG techniques are compared. These theoretical and experimental results confirm the validity and accuracy of the TIPTOE method for the multi-cycle laser pulses in UV, visible and IR wavelength ranges regardless of the duration of the laser pulse.
References [1] D. J. Kane et al., “Characterization of arbitrary femtosecond pulses using frequency-resolved optical gating,” IEEE J. Quantum Electron. 29, 571–579 (1993). [2] C. Iaconis et al., “Spectral phase interferometry for direct electric-field reconstruction of ultrashort optical pulses,” Opt. Lett. 23, 792–794 (1998). [3] M. Miranda et al., “Characterization of broadband few-cycle laser pulses with the d-scan technique,” Opt. Express 20, 18732–18743 (2012). [4] T. Brabec et al., “Intense few-cycle laser fields: Frontiers of nonlinear optics,” Rev. Mod. Phys. 72, 545–591 (2000). [5] E. Goulielmakis et al., “Direct Measurement of Light Waves,” Science 305, 1267–1269 (2004). [6] K. T. Kim et al., “Petahertz optical oscilloscope,” Nat. Photonics 7, 958–962 (2013). [7] A. S. Wyatt et al., “Attosecond sampling of arbitrary optical waveforms,” Optica 3, 303 (2016). [8] S. B Park et al., “Direct Sampling of a Light Wave in Air”, Optica (Accepted)
80 Tuesday
Prompt Dissociation of Metastable CO2+ in a Dimer
Xiaoyan Ding1, M. Haertelt1, S. Schlauderer1, M. S. Schuurman2,3, A. Yu. Naumov1, D. M. Villeneuve1, A. R. W. McKellar2, P. B. Corkum1, and A. Staudte1 1Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, Ottawa, Ontario, Canada K1A 0R6 2National Research Council, 100 Sussex Dr., Ottawa, Ontario, Canada K1A 0R6 3Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie, Ottawa, Canada K1N 6N5
We triply ionize the van der Waals bound carbon monoxide dimer with intense ultrashort pulses and study 3+ + + + the breakup channel (CO)2 →C +O +CO . The fragments are recorded in a cold target recoil ion momentum spectrometer. We observe a fast CO2+ dissociation channel in the dimer, which does not exist for the monomer. We found that a nearby charge breaks the symmetry of a X3Π state of CO2+ and induces an avoided crossing that allows a fast dissociation. Calculation on the full dimer complex shows the coupling of different charge states, as predicted from excimer theory, gives rise to electronic state components not present in the monomer, thereby enabling fast dissociation with higher kinetic energy release. These results demonstrate that the electronic structure of molecular cluster complexes can give rise to dynamics that is qualitatively different from that observed in the component monomers.
3+ + + + Figure 1. Newton diagram for all events in the channel (CO)2 → C + O + CO .
References [1] X. Ding, et al, “Ultrafast Dissociation of Metastable CO2+ in a Dimer,” Phys. Rev. Lett., 118, 153001 (2017).
81 Tuesday
Strong field stabilization and the excitation of neutral atoms in COLTRIMS
Zack Dube, Matthias Kuebel, Kyle Johnston, Tian Wang, Andrei Yu. Naumov, David M. Villeneuve, Paul B. Corkum, Andre Staudte Joint Attosecond Laboratory, National Research Council and University of Ottawa, Ottawa, Ontario, Canada K1A 0R6 [email protected]
A counter-intuitive consequence of using very high laser field strengths to study atoms is that the ionization rate can actually decrease with intensity. This may be explained by considering the motion of the electron in its reference frame - it is bound in the so called Kramers-Henneberger potential. These stable electrons are left in high lying Rydberg states post-pulse [1]. The first strong experimental evidence supporting the existence of Kramers-Henneberger stabilization was demonstrated in 2009 [2], and showed that neutral atoms in these states are also heavily accelerated by the ponderomotive force of the laser pulse. The existence of atoms stable under high field strengths can also be seen and studied in COLTRIMS experiments [3]. I will present the most recent results from our lab regarding Kramers-Henneberger stabilization and the acceleration of neutral atoms in a COLTRIMS apparatus.
References [1] F. Morales et al., “Imaging the Kramers-Henneberger atom,” PNAS 108, no. 41 (2011) [2] U. Eichman et al, “Acceleration of netural atoms in strong short-pulse laser fields,” Nature 461: 1261-1264 (2009) [3] S. Larimian et al, “Coincidence spectroscopy of high-lying Rydberg states produced in strong laser fields,” Physical Review A 94, 033401 (2016)
82 Tuesday
High-power, high-energy femtosecond laser systems for scientific and industrial applications
Sven Breitkopf, Tino Eidam, and Jens Limpert Active Fiber Systems GmbH, Wildenbruchstraße 15, 07745 Jena, Germany [email protected]
Active Fiber Systems GmbH (AFS) founded in 2009 is a spin-off from the Institute of Applied Physics in Jena and the Fraunhofer IOF Jena. The mission of AFS is to transfer groundbreaking experimental results to reliable turn-key laser systems suitable for scientific and industrial applications. Compact dimensions, considerably reduced production costs as well as flexible and outstanding laser parameters are among the extraordinary features of the fiber lasers from AFS. Based on unique technologies such as ytterbium-doped large-pitch fibers and multi-channel amplification in combination with coherent combination (see for example Fig. 1), AFS is able to offer femtosecond laser systems with up to 10 mJ of pulse energy and 1.4 kW of average power.
Fig. 1: High-power fiber-laser system with 6fs, 1mJ pulses at 100kHz repetition rate.
Even the most demanding applications can be addressed with additional options such as few- cycle pulse generation, CEP-stability and high-repetition-rate high-harmonic-generation (HHG). Resulting from the large average powers of the driving fiber laser, these table-top HHG sources (see Fig. 2) are able to offer highest photon fluxes beyond 1014 photons/s in a single harmonic.
Fig. 2: Fiber-based laser setup with pulse-compression stage and HHG chamber.
83 Tuesday
A Real-Space Perspective on High Harmonic Generation in Solids
Guilmot Ernotte1,*, Marco Taucer2, Paul B. Corkum1,2 1Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada 2National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada *[email protected]
High-harmonic generation (HHG) has been used for decades as an ultrafast tool to understand electron dynamics in atoms and molecules. Recent experiments have extended HHG in condensed matter. A clear similarity between the generation process of HHG in atoms and solids was found [1]. However, an important difference between the two processes is the delocalization of the electron. In atomic HHG, the electron must recombine with its parent ion, while in solids the delocalized nature of the electron in the conduction band allows it to recombine at a different lattice site from the one at which it was ionized. Usually, HHG in solids is described by solving the semiconductor Bloch equations in the basis of field- free Bloch states. Because these sates are the eigenstates of an infinite crystal, they are completely delocalized and hinder the understanding of the electron’s motion. We propose to use a localized basis of Wannier states to explore the role of different lattice recombination in HHG. Bloch states, ϕ푛, 푘(푥), and are characterized by the quantum numbers 푛 and 푘 representing the band and the quasi-crystal momentum respectively. We use these Bloch states to build the Wannier states as a coherent sum of the former with a linear phase 푘푙푎0 [2]:
휓 (푥) = 푑푘휙 (푥)exp (푖푘푙푎 ) (1) 훼,푙 ∫1BZ 훼,푘 0
They are characterized by the quantum number 푛 and 푙 and localized on lattice site 푙, at 푥 = 푙푎0, with a0 the lattice constant. We use this basis on a two-band system with an energy gap of 4 eV driven at 3 μm. The resulting harmonic spectrum can be decomposed into contributions from recombination across different numbers of lattice sites, ∆푙, as shown in Figure 1.
Figure 1: a) Wannier instantaneous energy levels as a function of different lattice position. The electric field bends the energy level into a ladder. Grey arrows represent recombination 5 lattices away. b) Sliding Fourier analysis of the high harmonic spectrum for the recombination 5 lattice away. The dashed line represents our semi-classical calculation.
References [1] G. Vampa, et al. “Linking high harmonics from gases and solids,” Nature, 522, 462, 2015. [2] W. Kohn, “Analytic properties of Bloch waves and Wannier functions,” Phys. Rev., 115, 809, 1959.
84 Tuesday
Background-Free Measurements of Autoionizing State Lifetimes in Krypton with Extreme Ultraviolet Wave Mixing
A. Fidler1,2, E. Warrick1,2, H. J. B. Marroux1,2, W. Cao1,2, D. M. Neumark1,2, S. R. Leone1,2.3 1Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 2Department of Chemistry, University of California, Berkeley, CA 94720 USA 3Department of Physics, University of California, Berkeley, CA 94720 USA [email protected]
With the advent of attosecond extreme ultraviolet (XUV) pulse generation techniques, the timescales of processes governed by electronic dynamics can now be measured directly in the time domain. These measurements are often complicated by overlapping spectral effects, impeding the quantitative retrieval of lifetimes associated with ultrafast processes [1]. By extending highly selective nonlinear wave mixing techniques developed in infrared and optical spectroscopies to the XUV regime [2], background-free 2 lifetime measurements of krypton’s ( P1/2)nd autoionizing states can be obtained. A noncollinear beam geometry between the XUV and near infrared (NIR) pulses capitalizes on the phase matching conditions inherent in wave mixing processes to isolate emission signals originating from the NIR-mediated coupling of XUV-generated autoionizing states to themselves through one photon dipole forbidden 2 ( P3/2)6p states. Examining these emission features as a function of XUV-NIR delay reveals dynamics 2 associated with the XUV-initiated electronic wavepacket (coherence) in the ( P1/2)nd autoionizing states. Due to the dominance of the degenerate, ac Stark-like pathway relative to other non-degenerate V-type coupling pathways, the 37±5 and 50±5 fs emission feature lifetimes measured at the energetic position of 2 2 the ( P1/2)7d and ( P1/2)8d autoionizing states are comparable to those calculated from linewidth 2 2 measurements of the ( P1/2)7d and ( P1/2)8d states [3]. This work represents a crucial step toward the development of a truly multidimensional XUV spectroscopy capable of assessing ultrafast dynamics in spectrally congested systems with unparalleled time resolution and specificity.
Figure 1: Four-wave mixing emission signals exhibit a complex time dependence indicative of the coherence 2 generated in the ( P1/2)nd states. The degenerate wave mixing pathway (left) results in the observed lifetime trend. References [1] X. Li et al., “Investigation of coupling mechanisms in attosecond transient absorption of autoionizing states: comparison of theory and experiment in xenon,” J. Phys. B: At. Mol. Opt. Phys. 48, 125601 (2015). [2] W. Cao et al., “Noncollinear wave mixing of attosecond XUV and few-cycle optical laser pulses in gas-phase atoms: Toward multidimensional spectroscopy involving XUV excitations,” Phys. Rev. A. 94, 053846 (2016 [3] K. Maeda et al., “High-resolution measurement for photoabsorption cross sections in the autoionization regions of Ar, Kr and Xe,” J. Phys. B: At. Mol. Opt. Phys. 26, 1541-1555 (1993).
85 Tuesday
Study and Applications of LIFT based mass spectrometry using ultrafast laser pulses
Alan Godfrey, Deepak Kallepalli, Andre Naumov, Paul B. Corkum Joint Attosecond Laboratory, National Research Council and University of Ottawa, Ottawa, Ontario, Canada K1A 0R6 [email protected], [email protected]
Applications of Laser Induced Forward Transfer (LIFT) are attractive and known in many fields, from laser printing of microelectronics to medical diagnostics. An ultrashort pulse (typically on the order of femtoseconds) can deposit energy locally leading to different types of modifications such as electrical, optical, chemical and physical. In particular attention to medical diagnostics, a cell/an organelle is required to be desorbed without being destroyed, to then perform medical diagnostics on that cell. Direct interaction of the cell/organelle with ultrafast laser may change its properties and hence, a buffer layer (or dynamic release layer) is placed in between the substrate and transfer material. Herein, we report our results on LIFTing a gold thin film to demonstrate the usefulness of the technique, which can then be integrated with a homebuilt mass spectrometer. We also show our results on the structural dynamics of a laser-modified dynamic release layer (polyimide). The laser causes intact protrusions to form in the polymer, which then thrust the material from the substrate during LIFT. The use of a femtosecond laser allows for nonlinear absorption of a pulse in the polymer, which can result in feature sizes under a wavelength.
Figure 1 – image of LIFTed gold thin film, for a fixed pulse energy of 300 nJ and varying position of the focusing optic, a 10x 0.2NA microscope objective. z=0 µm corresponds to precise focus of the laser on the dynamic release layer, and increasing z corresponds to retreating the focus from the dynamic release layer.
86 Tuesday
Two-cycle, 2.5 TW pulse generation at 1.8 μm via Frequency domain Optical Parametric Amplification
V. Gruson1,2, G. Ernotte1, P. Lassonde1, L. Di Mauro2, P. Corkum3, H. Ibrahim1, B. Schmidt1,4, F. Légaré1 1Institut National de la Recherche Scientifique, Centre Énergie Matériaux et Télécommunications, 1650 Boulevard Lionel-Boulet, Varennes, Quebec, Canada J3X1S2 2Department of Physics, The Ohio State University, 191 West Woodruff Ave, Columbus, OH 43210, USA 3Joint Attosecond Science Laboratory, University of Ottawa and National Research Council of Canada, 100 Sussex Dr, Ottawa, ON K1N 5A2, Canada 4few-cycle Inc., 2890 Rue de Beaurivage, Montreal, Quebec, Canada H1L 5W5 [email protected]
Recently, Frequency domain Optical Parametric Amplification (FOPA, [1, 2]) appeared as a new ultrabroadband amplification scheme. Here, we extend its capability to amplify a 1.2 mJ, 14 fs, 1.8 µm source up to 30 mJ while conserving its properties [3]. Figure 1 (a) shows the layout of the developed FOPA, while Figure 1 (b) and (c) show the temporal characterization, before and after amplification, with the reconstructed pulse showing that the temporal properties are conserved after amplification.
Fig.1. (a) FOPA layout. The seed pulses enter the FOPA from the left side. Angular dispersion is applied through the grating G1, giving rise to a horizontal spatial separation of the different spectral components. Next, the spectrally separated components are collimated after reflection on a cylindrical mirror (M1, f=+60 cm), focusing only in the horizontal direction of the Fourier Plane (FP) to generate narrowband pulses of 2.5 ps duration. Here, broadband phase-matching from 1.4 to 2.2 μm can be achieved using two BBO crystals of 6 mm thickness. The FP is pumped by 240 mJ, 0.8 μm, 2.5 ps pulses at 10Hz. The pump has a spatial top-hat shape to ensure homogeneous amplification across the FP. The amplified beam is then recombined by refocusing using an identical cylindrical mirror M2 and by applying an opposite angular dispersion using grating G2. (b-c) Temporal characterization. SHG-FROG Traces obtained (b) before and (c) after amplification, with their respective reconstructed pulses, showing a pulse duration of 12fs FWHM. To conclude, FOPA provides an efficient and robust approach for scaling few-cycle IR source to few TW peak power. Furthermore, the currently used BBO crystals (20×15 mm) are not the largest commercially available, more than two could be used, thus paving the route for scaling FOPA to >10 TW peak power.
References [1] B. E. Schmidt, N. Thiré, et al., “Frequency domain optical parametric amplification”, Nature Communications, 5, (2014). [2] P. Lassonde, N. Thiré, et al., “High gain frequency domain optical parametric amplification”, IEEE Journal of Selected Topics in Quantum Electronics, 21(5):1–10, (2015). [3] V. Gruson, G. Ernotte, et al., “2.5 TW, two-cycle IR laser pulses via frequency domain optical parametric amplification”, Opt. Express 25, 27706-27714 (2017)
87 Tuesday
Controlled energy deposition in micromachining by using two femtosecond laser pulses
Ziyue Guo*, Kailin Hu, Tao Cao, Le Huang, Yu Chen, Xuanchao Qin, Shaozhen Liu, Jikun Yan, and Jiahui Peng School of Optical and Electronic Information, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, China, 430074 * [email protected]
Nowadays, femtosecond laser micromachining of transparent materials are widely applied in consumer electronics [1], and it is very hard to find a stocked femtosecond laser in China in the first quarter of this year. For femtosecond laser micromachining, energy is absorbed by the free carriers in solids in a process that is much faster than the process of energy being transferred via heating, thus resulted in better machining qualities. Furthermore, because of the nonlinear nature of the multiphoton absorption, femtosecond laser micromachining is a relatively deterministic process, which makes the machining qualities stable and consistent [2]. However, when a single femtosecond pulses being used, high precision and small feature size are incompatible with large throughout fabrication during the process of micromachining. On the spatial front, the smallest feature is determined by the diffraction limit of the femtosecond laser. On the energy front, the energy that can be deposited is limited by nonlinear absorption [3]. Attempts to deposit more energy by simply increasing pulse intensities will degrade the spatial resolution rather than enhance the machining efficiency. Based on the dilemma above, Paul Corkum proposed double-pulse method [4], which provides the freedom to control the spatial resolution and deposited energy density independently. Besides, adjustable pulse duration, wavelength, energy, polarization and the time delay between the two pulses allow control of energy deposition via wide parameter space. Meanwhile, the obtained results are of fundamental relevance to many applications where tightly focused femtosecond laser pulses are used.
Fig.1 Experiment setup. Fig.2 Transmission of the driving pulse as a function of energy for different pulse durations
References [1] E. Mazur, et al. “Femtosecond laser micromachining in transparent materials,” Nature Photon.2, 219-225(2008). [2] B. C. Stuart, et al. “Nanosecond-to-femtosecond laser-induced breakdown in dielectrics,” Phys. Rev. B 53, 1749-1761(1996). [3] D. M. Rayner, et al. “Ultrashort pulse nonlinear optical absorption in transparent media,” Opt. Express 13, 3208(2005) [4] Peng, J, et al. “Control of energy deposition in femtosecond laser dielectric interactions,” Applied Physics Letters 102, 161105(2013).
88 Tuesday
Light amplification by seeded Kerr instability
T.J. Hammond1,2, G. Vampa1,2,3, M. Nesrallah1, A. Yu. Naumov1,2, P.B. Corkum1,2, and T. Brabec1 1Department of Physics, University of Ottawa, Ottawa, ON K1N 6N5, Canada 2National Research Council of Canada, Ottawa, ON K1A 0R6, Canada 3Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA [email protected], [email protected]
We demonstrate amplification from the visible to the infrared (0.5 to >2 µm) by seeding the modulation instability in a single Y3Al5O12 (YAG) crystal. By pumping with femtosecond near-infrared pulses we are able to achieve gain factors >1000 – up to 1 TW/cm2 – while maintaining the seed temporal and beam profiles, ideal for studying strong-field processes in condensed matter. Kerr instability amplification avoids constraints of doping and phase matching, opening a path to far-infrared amplification.
References [1] G. Vampa, T. J. Hammond, M. Nesrallah, A. Yu Naumov, P. B. Corkum, T. Brabec. Light Amplification by Seeded Kerr Instability. Science 359, 673–675 (2018). [2] M. Nesrallah, G. Vampa, G. Bart, P. B. Corkum, C. R. McDonald, T. Brabec. Theory of Kerr instability amplification. Optica 5, 271–278 (2018).
89
ABSTRACTS – POSTERS Wednesday, May 9, 2018
Wednesday
Where Do They Go? Proton Migration in Hydrocarbons
H. Ibrahim1*, B. Wales2, S. Beaulieu1, V. Wanie1, M.S. Schuurman3, J. Sanderson2, and F. Légaré1 1INRS-EMT, 1650 Blvd. Lionel-Boulet, Varennes Quebec Canada J3X 1S2 2University of Waterloo, 200 University Av. W., Waterloo, Ontario, Canada N2L 3G1 3NRC, 100 Sussex Dr., Ottawa, Ontario, Canada K1A 0R6
The role of mass differences and slight changes in molecular geometry will be discussed based on the comparison of isomerization dynamics in the small hydrocarbon molecule acetylene (C2H2 and C2D2) as well as ethylene (C2H4). How does doubling the mass of the moving atom influences isomerization time and yield when exchanging H+ by D+? What is the role of the conical intersection? The uncommon excitation regime of strong field multi-photon ionization allows us to study these dynamics in a table-top setup, taking advantage of rather high repetition rates and temporal resolution. The dynamics is imaged based on two- or three-body correlations of fragments obtained with the Coulomb Explosion Imaging technique. Especially the ethylene molecule reveals rich ultrafast dynamics in its various breakup channels – the symmetric as well as the asymmetric ones.
Figure 1: Scheme of cation isomerization dynamics initiated by strong field multi-photon ionization (4 photons at 266nm). Linear molecular structure appears on the left hand side, y-shaped structure on the right hand side and the transition state is located at the region of the conical intersection.
References [1] H.Ibrahim et al., “Tabletop imaging of structural evolutions in chemical reactions demonstrated for the acetylene cation,” nature comms. 5:4422 (2014). [2] H. Ibrahim, et al., “Isotope Effect in the three Break-up Channels of the Acetylene Cation,” International Conference on Ultrafast Phenomena, OSA Technical Digest (online) (Optical Society of America, 2016), paper UF2A.3.
92 Wednesday
Holographic Measurement of Time-dependent Optical Fields
Dong Hyuk Ko, Graham Brown, Fanqi Kong, Chunmei Zhang and Paul Corkum Joint Attosecond Science Laboratory, University of Ottawa and National Research Council, Canada [email protected]
We demonstrated holographic measurement of attosecond high harmonic pulses and a femtosecond laser pulses in order to characterize time-dependent optical fields. To achieve this, we introduced a weak laser field into the harmonic generation medium together with the strong driving laser field [1,2]. The weak laser field perturbed the trajectories of ionized electrons periodically, which are exquisite for generating high harmonics. Since the periodic modulation in the near-field dipole emissions implies cross-correlation of the attosecond pulse and the perturbing laser pulse, we could achieve temporal characterization by measuring the diffracted high harmonic radiations at far field. We superposed a reference X-ray beam generated from another source because the far-field intensity distribution is insensitive to the near-field dipole emissions [3]. The spectrally resolved harmonic image showed dense fringes due to the two-source interference. These fringes hold the phase information of the high harmonic radiations, which enabled us to reconstruct the near-field dipole emissions in time [4]. Therefore, we characterized the attosecond pulses, showing a pulse duration of 390 as, and the time- dependent electric field of the perturbing laser pulse from the retrieved near-field image [5]. The duration of the perturbing pulse that we obtained was consistent with the result achieved by a conventional second harmonic FROG measurement. The holographic pulse measurement is a fast and effective way to monitor attosecond pulses in soft X-ray region. Eventually, it will be a new method to probe ultrafast strong-field dynamics in many materials.
References [1] N. Dudovich et al., “Measuring and controlling the birth of attosecond XUV pulses,” Nature Phys. 2, 781-786 (2006). [2] K. T. Kim et al., “Manipulation of quantum paths for space-time characterization of attosecond pulses,” Nature Phys. 9, 159-163 (2013). [3] J. B. Bertrand et al., “Linked attosecond phase interferometry for molecular frame measurements,” Nature Phys. 9, 174-178 (2013). [4] S. Eisebitt et al., “Lensless imaging of magnetic nanostructures by X-ray spectro-holography,” Nature 432, 885-888 (2004). [5] K. T. Kim et al., “Petahertz optical oscilloscope,” Nature Photon. 7, 958-962 (2013).
93 Wednesday
Selectivity of electronic coherence and attosecond ionization delays in strong-field double ionization
Yuki Kobayashi1,*, Maurizio Reduzzi1, Kristina F. Chang1, Henry Timmers1, Daniel M. Neumark1,2, and Stephen R. Leone1,2,3 1Department of Chemistry, University of California, Berkeley, California 94720, USA 2Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 31Department of Physics, University of California, Berkeley, California 94720, USA *[email protected]
Interactions between intense laser electric fields and atoms induce plethora of unique phenomena such as non-sequential double ionization and high-harmonic generation [1]. Recent attosecond experiments demonstrated that few-cycle intense laser pulses create electronic coherence in ionic valence states of rare-gas atoms [2]. Here we perform attosecond transient-absorption spectroscopy on xenon atoms and investigate coherent electron dynamics in the multiple-ionization intensity regime. Experimentally, 3.5-fs NIR pulses with a peak intensity at 7x1014 W/cm2 ionize electrons from the 5p valence shell, and subsequent 200-as XUV pulses probe the valence dynamics by 4d-5p core-to-valence excitation. Delay-dependent transient-absorption spectra are shown in Fig. 1(a). Quantum beats with 4.1- fs oscillation period are observed in the Xe2+ signals, indicating an electronic coherence formed in the ions. Absorption spectra are simulated using a density-matrix based method [3], and the observed 3 0 3 0 2+ coherence is assigned to be between P2 - P0 of Xe at a degree of coherence g = 0.4. Ionization delays between Xe+ and Xe2+ are also evaluated based on the rise of the spectral lineouts (Figs 1(b)-(d)). The 3 3 3 2+ 2 + ionization delays for P2, P0, P1 of Xe , with respect to P3/2 of Xe , are 0.85 fs, 0.64 fs, and 0.75 fs, respectively. The measured delays are shorter than half of the optical cycle, indicating a major contribution of double ionization within one laser half-cycle. Strong-field double ionization is simulated using an uncorrelated electron-emission model. The simulated results predict multiple coherences to be observed in Xe+ and Xe2+ in contrast to the selective result of the experiments. Ionization delays are predicted to be almost equal to half of the laser optical cycle. The contrast between the experiments and simulations suggests a larger role of electron correlation in strong- field double ionization.
Figure 1 (a) Delay-dependent transient-absorption spectra. (b) State-resolved spectral lineouts of Xe+ and Xe2+. Measured ionization delays are denoted below the state labels.
References [1] P. B. Corkum “Plasma perspective on strong field multiple ionization,” Phys. Rev. Lett. 71, 1994 (1993). [2] E. Goulielmakis, et al., “Real time tracing of valence-shell electronic coherences with attosecond transient absorption spectroscopy,” Nature 466, 739 (2010). [3] R. Santra, et al., “Theory of attosecond transient absorption spectroscopy of strong-field-generated ions,” Phys. Rev. A 83, 033405 (2011).
94 Wednesday
Streak Camera for Strong-Field Ionization
Matthias Kübel1,2, Andrei Yu. Naumov1, David M. Villeneuve1, Paul B. Corkum1, André Staudte1 1Joint Attosecond Laboratory, National Research Council and University of Ottawa, Ottawa, Canada 2Ludwig-Maximilians-Universität München, Am Coulombwall 1, Garching, Germany [email protected]
The attosecond streak camera has permitted deep insights into the ultrafast dynamics of electrons in atoms [1], molecules [2] and solids [3] using weak-field photoionization. Here, we introduce a streak camera for strong-field ionization [4] that I call STIER (= Subcycle Tracing of Ionization Enabled by infraRed). The method relies on ionization by an intense visible few-cycle pulse, and deflection of the generated photoelectrons by a phase-stable mid-infrared field of moderate intensity. Figure 1 shows an exemplary STIER trace.
Fig. 1. STIER trace recorded for Neon ions generated by an intense few-cycle pulse (735 nm, 7×1014 Wcm-2, 5 fs) in the presence of a phase-stable IR field (2215 nm, 3×1013 Wcm-2). The solid (dashed) black line show the relative ionization yields measured for CEP stable visible pulses with ϕ = 0 (ϕ = π).
We will show that STIER can image the individual ionization bursts produced at the peaks of the electric field of a phase-stable few-cycle laser pulse. This capability enables insights into sub-cycle dynamics of ionization, where significant forward scattering of low-energy electrons is observed. STIER may further provide answers to questions regarding strong-field ionization time delays, tunneling momentum distributions, and frustrated ionization. Tuning the polarizations, phases, and amplitudes of the optical laser fields used in STIER, opens up a large number of applications in strong-field (attosecond) physics of atoms, molecules and solids. We will present unpublished experimental results on imaging and controlling strong-field ionization of atoms, 4D imaging of an oscillating valence electron density, and coherent control of molecular dissociation using STIER.
References [1] R. Kienberger, et al. Nature 427, 817 (2004). [2] G. Sansone, et al. Nature 465, 763 (2010). [3] A. L. Cavalieri, et al. Nature 449, 1029 (2007). [4] M. Kübel, et al. Phys. Rev. Lett. 119, 183201 (2017).
95 Wednesday
Insulator-to-semimetal transition of dielectric crystals under strong optical fields
Ojoon Kwon1,2†, Vadym Apalkov3, Mark I. Stockman3, D. Kim1,2 1 Department of Physics, Center for Attosecond Science and Technology, Pohang University of Science and Technology, Pohang, 37673, Republic of Korea 2 Max Planck Center for Attosecond Science, Max Planck POSTECH/Korea Res. Init., Pohang, 37673, Republic of Korea. 3Center for Nano-Optics (CeNO) and Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA † current address : Institut National de la Recherche Scientifique, Centre Énergie Matériaux et Télécommunications, 1650 Boulevard Lionel-Boulet, Varennes, Quebec, Canada J3X1S2 [email protected]
Interaction of light with matter is a topic of long history. In the era of modern science, owing to the development and evolution of laser, controlling characteristics of material by means of light has been under intensive investigation. In particular, inducing electric current in dielectric medium using state-of- the-art waveform-controllable laser field has recently been demonstrated [1]. It has substantially impacted as it is not only intriguing to scientists but also possesses potential for application in information technology [2]. Here I present the response of dielectric crystals to intense optical field. Under the strong laser field, insulating media undergo semi-metallization, which allows electric current to flow through. Since the directionality of the light-induced current is in accordance with that of the impinging laser field, the instantaneous field of the laser is responsible for the current. By measuring the temporal profile of the current, the timescale for the transition from insulator to semimetal is verified to be sub-femtosecond. Different species of crystals, quartz, sapphire and calcium fluoride, are comparatively studied. Despite the dissimilarities among them, qualitatively alike behavior is exhibited. The resemblance is interpreted as a consequence of Wannier-Stark localization, by which the electrons in periodic lattice subjected to strong electric field are imprisoned within a unit cell. This prevents the electrons from ‘feeling’ crystallographic nature of each material, leading to indistinguishability.
References [1] A. schiffrin et al. “Optical-field-induced current in dielectrics,” Nature 493 70-74 (2013) [2] F. Krausz et al. “Attosecond metrology: from electron capture to future signal processing,” Nat. Photonics 8, 205–213 (2014).
96 Wednesday
+ Testing the role of recollision in N2 air lasing Patrick Laferrière1, Mathew Britton1, Ladan Arissian1,2,3, and P.B. Corkum1,2 1Department of Physics, University of Ottawa, Ottawa, Ontario, Canada 2National Research Council of Canada, Ottawa, Ontario, Canada 3University of New Mexico, Albuquerque, New Mexico, USA [email protected]
We investigate the lasing dynamics of the molecular nitrogen cation ("air lasing") induced by strong field + laser pulses. The mechanism behind the N2 air laser is still under debate and recollision has been proposed as the dominant mechanism[1]. To study the role of recollision, we measure the ellipticity dependence of the gain in two media. We start by focusing femtosecond laser pulses in ambient air to study the gain in an air filament. We then employ a pump-probe scheme and focus in a supersonic gas jet in a vacuum, with the width of the jet chosen such that the B-integral is small, thus removing the complexity of filamentation. We observe an enhancement of the gain with nonzero ellipticity in air filamentation for the transitions ν = 0 → ν = 0 (391 nm) and ν = 0 → ν = 1 (428 nm) between the B and X states, as previously reported [1]. We find that the ellipticity dependence of the gain still shows an enhancement with nonzero ellipticity after accounting for the ellipticity dependence of the continuum around the emission lines (see Figure 1 (a)). This is evidence that the ellipticity dependence is intrinsic to the gain mechanism and not just the seed. We make similar measurements under more controlled conditions in a gas jet in a vacuum chamber. This setup enables a direct connection to high harmonic generation, where recollision dominates. We observe a similar enhancement with nonzero pump ellipticity for both the 391 nm and 428 nm gain, and significant gain for a circular pump polarization. The measured intensity of the high harmonics generated by the pump beam shows a rapid decrease with increasing ellipticity. Figure 1 (b) shows a comparison of the + gain in N2 and the generated harmonics. Significant gain is measured while recollision is suppressed by ellipticity; therefore, we conclude that recollision does not play a significant role in the gain dynamics of + the N2 air laser.
Figure 1: (a) Ellipticity dependence of the gain at 428 nm, the continuum next to the gain, and the 428 nm intensity divided by the continuum next to the emission. (b) Normalized gain at 391 and 428 nm as a function of ellipticity and the high harmonics (H11-H21) also as a function of ellipticity.
References [1] Y. Liu et al., “Recollision-Induced Superradiance of Ionized Nitrogen Molecules” Phys. Rev. Lett. 115, 133203 (2015)
97 Wednesday
Amplitude and phase transfer in Fourier-domain nonlinear optics
Philippe Lassonde1*, Bruno E. Schmidt2, Guilmot Ernotte1, Matteo Clerici3, Roberto Morandotti1, Heide Ibrahim1 and Francois Légaré1* 1INRS-emt, 1650 blvd Lionel-Boulet, Varennes, QC, J3X 1S2, Canada 2Few-cycle inc., 2890 Rue de Beaurivage, Montreal, H1L 5W5, QC, Canada 3University of Glasgow, School of Engineering, G12 8QQ, Glasgow, United Kingdom * [email protected]; [email protected]
When considering nonlinear processes with ultrashort laser pulses, the medium response depends on the temporal intensity distribution. A consequence is that the out coming field is problematic to control since it highly depends on the spectral phase distribution of the incoming field. In this paper, we demonstrate an original scheme of nonlinear interaction enabling to decouple frequencies, amplitude and phase and giving a high level of control over the field resulting from a nonlinear interaction. In a similar manner, optical Fourier transformation was employed to facilitate parametric amplification of few-cycle pulses in the frequency domain, instead of the time domain [1]. Here, we expand on this strategy and introduce a generalized view on performing nonlinear optics in the frequency domain [2]. By Fourier transforming an ultrashort laser pulse, we were able to decouple the spectral amplitude and phase coupling that is inherent to nonlinear processes performed in time domain. In this manner, frequency domain nonlinear optics enables the generation of new light fields with properties previously inaccessible by time domain interactions. By using this scheme, we were able to perform pulse shaping in the deep UV at 207 nm by direct spectral phase transfer from the fundamental to the fourth-harmonic field.
References [1] B.E. Schmidt, N. Thiré, M. Boivin, A. Laramée, F. Poitras, G. Lebrun, T. Ozaki, H. Ibrahim, F. Légaré, Frequency domain optical parametric amplification, Nat Commun, 5 (2014). [2] B.E. Schmidt, P. Lassonde, G. Ernotte, M. Clerici, R. Morandotti, H. Ibrahim, F. Légaré, Decoupling Frequencies, Amplitudes and Phases in Nonlinear Optics, Scientific Reports, 7, 7861 (2017).
98 Wednesday
Spatial properties of high harmonic beams from plasma mirrors
A. Leblanc, S. Monchocé, H. Vincenti, S. Kahaly, J-L. Vay, and F.Quéré Lasers, Interactions and Dynamics Laboratory, Commissariat à l'Energie Atomique, Saclay, 91191 Gif sur Yvette,France.
A scheme is developed to retrieve the spatial amplitude and phase profiles of high order harmonics generated on plasma mirrors directly in the target plane. It is used to validate analytical models of laser-plasma interaction. When focusing an ultra-intense femtosecond laser pulse (I > 1016 W/cm2) onto a solid target, this target is ionized at the very beginning of the laser pulse. The resulting dense plasma reflects the laser in the specular direction: it is called a plasma mirror. The ultra-intense laser field can accelerate electrons within the plasma at relativistic speeds at each optical cycle resulting in periodic Extreme UltraViolet radiation. Those trains of attosecond pulses, generated in the specular direction, are associated with the generation of high-order harmonics of the laser pulsation. Two main HHG processes on solid targets have been observed for different interaction conditions. At moderate laser intensities (I < 1018 W/cm2), Brunel electrons are accelerated into the target, exciting plasma oscillations on their way in the high density plasma gradient, which radiate at the local plasma frequency. It is the Coherent Wake Emission (CWE) process. At ultra-high intensities (I > 1018 W/cm2), the electron density of the plasma oscillates normally to the target with a relativistic velocity under the effect of the incoming laser field. It changes the shape of the reflected field by a periodic Doppler effect: this is the Relativistic Oscillating Mirror (ROM) process. Those two processes carry rich information on the laser-plasma interaction. For instance, as shown by PIC simulations on the fig. 1, the spatial curvature of each emitted attosecond pulse directly results from the interaction properties: the spatial curvature of the plasma oscillations into the plasma gradient for the CWE process, and the spatial curvature of the plasma surface under radiation pressure for the ROM process. However, measuring the harmonic spatial curvature directly in the target plane is very challenging: due to the extreme physical condition in the interaction region, the detection can only be done at macroscopic distances from target. It was made possible by adapting a technique of coherent diffraction imaging, named ptychography, which consists in measuring diffraction patterns resulting from a probe beam diffracted on an object for different relative positions of one to the other [1]. This technique was transposed to HHG on solid target by spatially microstructuring the target with a pre-pulse which ionizes the target typically few picoseconds before the main pulse driving HHG. Harmonic fields in the target plane are then reconstructed spatially in amplitude and phase [2]. This new technique is used to study of the harmonic spatial properties in different interaction conditions for the two HHG processes. Thanks to this parametric study, previously developed analytical models of the interaction in the non-relativistic and relativistic regimes are experimentally validated [3]. Its accuracy is also used to test different numerical schemes of Maxwell’s equations solvers in PIC simulations. Fig 1 – PIC simulations of the interaction of an intense laser beam with a plasma mirror. The electron density is shown in grey scale and the attosecond pulses emitted in purple scale. a - CWE case : a0=0.4, L=λ/30; b - ROM case, a0=3, L=λ/10.
References [1] Optically controlled solid-density transient plasma gratings, Monchocé et al, PRL 112, 145008, (2014) [2] Ptychographic measurements of ultrahigh-intensity laser-plasma interactions, Leblanc et al, Nat. Phys. 12 301 (2016). [3] Spatial properties of high-order harmonic beams from plasma mirrors: a ptychographic study, Leblanc et al, PRL 119 155001 (2017)
99 Wednesday
High Harmonics Sources for Probing Ultrafast Optical Demagnetization in Multilayer Films
Katherine Légaré1, Vincent Cardin1, Tadas Balciunas2, Guangyu Fan2, Nicolas Jaouen3, Jan Lüning4, Andrius Baltuska2, and François Légaré1 1INRS, Centre EMT, 1650 boulevard Lionel-Boulet, Varennes (Québec) J3X 1S2, Canada 2Institute of Photonics, Vienna University of Technology, Gusshausstrasse 27-387, 1040 Vienna, Austria 3Synchrotron SOLEIL, Saint-Aubin, Boite Postale 48, 91192 Gif-sur-Yvette Cedex, France 4Sorbonne Universités, UPMC Univ. Paris 06, CNRS, Laboratoire de Chimie Physique – Matière et Rayonnement, 75005 Paris, France [email protected]
The discovery of the ultrafast optical demagnetization by Beaurepaire et al. [1], in 1996, has paved the way to faster data manipulation [2]. The rapidity of the magnetization reversal induced by short laser pulses could push the limits of magnetic spin switching to femtosecond timescales and allow for high- density magnetic data storage devices driven by optical methods [2]. This has since been a motivation for extensive investigation of ultrafast demagnetization. It is understood that the process consists of three steps of thermalization. The electrons are first heated by the optical pulse and then successively thermalize with the spin system, the lattice and the surrounding metals. However, the underlaying mechanisms of the energy transfer in the first steps are still being debated. It is therefore essential to design new experimental schemes to probe this phenomenon in unique ways. These time-resolved and element-specific experiments require access to a femtosecond XUV or soft X-ray source, which can be provided by free-electron lasers [3], synchrotron radiation femtoslicing [4] or high-order harmonic generation (HHG). The latter offers the advantages of being a table-top source with high temporal resolution. Furthermore, both the pump and the probe can come from the same laser source, producing a jitter free experiment. We make use of the HHG source of the Advanced Laser Light Source (ALLS) laboratory to probe ultrafast optical demagnetization at the M-edge of cobalt (around 60 eV) by resonant magnetic X-ray scattering (RMXS) [5]. The sample studied is a [Co/Pt] multilayer film in which the magnetic domains present out-of-plane magnetization vectors. When a XUV source tuned to 60 eV is transmitted through the sample, light scattering occurs on the magnetic centers. The intensity of the resulting diffraction peaks is related to the magnetization vector's amplitude. Demagnetization curves are obtained with an infrared pump - XUV probe scheme. RMXS is preferred to other techniques since it doesn’t require circularly polarized harmonics, which means it can be scaled to probe more energetic edges as harmonic sources improve. This scheme was also used in Vienna, where Prof. Baltuska and his group developed a harmonic source driven by an Yb laser that can reach the N-edge of rare-earths, making it possible to probe ultrafast demagnetization in Terbium (155 eV). With the high availability and versatility of table-top sources, we will be able to engineer many experiments to further investigate this phenomenon in the future.
References [1] E. Beaurepaire et al., “Ultrafast spin dynamics in ferromagnetic nickel,” Phys. Rev. Lett. 76, 4250–4253 (1996). [2] T. Li et al., “Femtosecond switching of magnetism via strongly correlated spincharge quantum excitations,” Nature 496, 69–73 (2013). [3] S. Düsterer et al., “Femtosecond x-ray pulse length characterization at the linac coherent light source free electron laser,” New J. Physics 13 (2011). [4] R. W. Schoenlein et al., “Generation of femtosecond pulses of synchrotron radiation,” Science 287, 2237–2240 (2000). [5] B. Vodungbo et al., “Laser-induced ultrafast demagnetization in the presence of a nanoscale magnetic domain network,” Nat. Commun. 3 (2012).
100 Wednesday
XUV Transient Absorption of Pre-aligned N2 molecules Peng Peng, Claude Marceau, A. Yu. Naumov, P. B. Corkum, D. M. Villeneuve Joint Attosecond Science Laboratory, National Research Council of Canada and University of Ottawa, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada [email protected]
Attosecond transient-absorption spectroscopy (ATAS) allows simultaneous observation of time- dependent dynamics of both bound and continuum states. Recently this method has been applied to study molecular systems [1–6]. In this work, we show how light-induced transitions in N2 molecules can efficiently be controlled by impulsive alignment. A short intense laser pulse is used to create rotational wave packet of N2 molecules. After the extinction of the field, the periodic rephasing and dephasing of the rotational eigenstates leads to a temporal revival structure of molecular alignment and antialignment. A time delayed broadband (13-24 eV) XUV pulse is used to study transient absorption spectroscopy. The measured absorption spectrum shows modulation when we change the time delay. Parallel (perpendicular) transitions show modulation in (out of) phase with alignment degree.
2 Fig. 1 (a) Calculated alignment degree
References [1] E. R. Warrick et al. “Probing the Dynamics of Rydberg and Valence States of Molecular Nitrogen with Attosecond Transient Absorption Spectroscopy,” J. Phys. Chem. A 120, 3165−3174 (2016). [2] E. R. Warrick et al. “Attosecond transient absorption spectroscopy of molecular nitrogen: Vibrational coherences in the b’1Σu+ state,” Chem. Phys. Lett. 683, 408 (2017). [3] M. Reduzzi et al. “Observation of autoionization dynamics and sub-cycle quantum beating in electronic molecular wave packets,” J. Phys. B 49, 065102 (2016). [4] Y. Cheng et al. “Reconstruction of an excited-state molecular wave packet with attosecond transient absorption spectroscopy,” Phys. Rev. A 94, 023403 (2016). [5] C. T. Liao et al. “Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic-symmetry-dependent line shapes and laser-induced modification,” Phys. Rev. A 95, 043427 (2017). [6] Wei Cao et al. “Excited-state vibronic wave-packet dynamics in H2 probed by XUV transient four-wave mixing,” Phys. Rev. A 97, 023401 (2018).
101 Wednesday
Compression of femtosecond electron pulses using tightly focused terahertz waves
Simon Robitaille* and Michel Piché Centre d’optique, photonique et laser, Université Laval, 2375 de la Terrasse, Québec, Québec G1V 0A6, Canada *[email protected]
The longitudinal electric field component of intense, few-cycle, radially-polarized laser beams can generate and accelerate electron pulses suitable for ultrafast electron diffraction [1-2]. However, after acceleration, the electron pulse duration increases during propagation to a target due to velocity dispersion. In this presentation, we describe how intense terahertz waves can be used to recompress femtosecond electron pulses. This approach may be an alternative to the scheme based on radio frequency cavity often used for electron pulse compression. To compress a stretched electron pulse, the electrons trailing at the end of the pulse must be accelerated and/or those at the front of the pulse must be slowed down. Using numerical simulations, we show that this velocity inversion can be achieved using strongly focused terahertz waves in the LP01 mode [3]. The terahertz field is a standing wave along the z-axis while the electrons propagate along the x-axis; its wavelength is 300 μm and it is focused to a spot size of ~1 λ. Space charge effects are neglected. As initial condition in our simulations, we consider a typical electron pulse produced by direct-field acceleration with 230-keV energy and a FWHM width along the x-axis of 4.16 μm, corresponding to a 2-fs duration [2]. After propagating over 0.8 mm, the electron pulse duration has increased to 46 fs. By synchronizing the terahertz wave with the electron pulse at this position, the terahertz electric field accelerates the electrons at the tail of the pulse. A few picoseconds later, the electron pulse duration is reduced to 8 fs when the electric field amplitude is 10 GV/m. Using the same terahertz wave but with a weaker electric field (1 GV/m), a 40-keV, 330-fs electron pulse can be compressed to 120 fs. Other examples of electron pulse compression will be presented.
Figure 1. Dispersion of a 2 fs electron pulse and its compression to a width of 8 fs using a terahertz wave.
References [1] C. Varin et M. Piché. Relativistic attosecond electron pulses from a free-space laser-acceleration scheme," Phys. Rev. E 74, 045602(R) (2006). [2] V. Marceau et al. Femtosecond 240-keV electron pulses from direct laser acceleration in a low-density gas, Phys. Rev. Lett. 111, 224801 (2013). [3]A. April, “Ultrashort, strongly focused laser pulses in free space,” in Coherence and Ultrashort Pulse Laser Emission, F. J. Duarte, ed., InTech, 355–382 (2010).
102 Wednesday
IR Peak Power & Average Power scaling via (FOPA)
B. E. Schmidt1, V. Gruson2,3, P. Lassonde2, G. Ernotte2, H. Ibrahim2, D. Ferachou1,2, A. Hage4, T. Mans4, L. Di Mauro3, P. B. Corkum5, H. J. Wörner6, and F. Légaré2 1few-cycle Inc., 2890 Rue de Beaurivage, Montreal, H1L 5W5, Qc, Canada 2INRS-EMT, 1650 Blvd. Lionel Boulet, Varennes, J3X 1S2, Qc, Canada 3Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA. 4Amphos GmbH, Kaiserstraße 100, 52134 Herzogenrath, Germany 5Joint Attosecond Science Laboratory, University of Ottawa &National Research Council of Canada, 100 Sussex Dr, Ottawa K1N 5A2, Canada 6ETH – Zürich, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland [email protected], [email protected]
One important application of Fourier domain nonlinear optics [1] is the optical parametric amplification of few-cycle pulses with FOPA [2]. It enables simultaneous upscaling of pulse energy and bandwidth while this denotes a trade-off for its time domain counterparts like OPCPA. Another grand challenge in contemporary laser science is average power scaling. We will discuss our progress on both FOPA design for high energy operation and the average power boosting based on an Yb Innoslab pump laser. We will present experimental results for high peak power IR pulses in the 2-cycle regime at 1.8 µm wavelength carrying 30 mJ of pulse energy (> 2 TW). Furthermore, we present a 500 W average power Yb pump laser with 50 mJ pulse energy at 10 kHz repetition rate and 1.5 ps pulse duration. The peak power scaling of few-cycle pulses is largely facilitated by
the separation ansatz of FOPA which allows one to break down a big task into smaller sub-problems. Due to frequencies’s spatial Fig. 1: a) & b) Far field beam properties of the separation in the Fourier plane (FP) of a 4f setup the amplifier 2.3 TW FOPA at 1.8 µm wavelength. c) & d) SHG- output properties are not restricted by the performance of a single FROG trace and autocorrelation of the 2-cycle crystal but by the number of different individually optimized FOPA output at 1.8µm wavelength at maximum crystals. Figure 1 summarizes results obtained from a two-crystal amplification. FOPA pumped by a ps TiSa beam carrying 250 mJ of energy. It was stretched to about 2.5 ps to match the duration of the seed in the FP. From figures 1 (a) & (b) show that the spatial and temporal properties are maintained after amplification up to 2.3 TW at 1.8 µm wavelength. We will present first HHG results with the new high power beam line at the attosecond conference. To achieve average power scaling, we moved from the TiSa pumping to an Yb Innoslab laser (Amphos GmbH) because of the superior thermal properties of the crystal host material. The main advantages of this type of pump laser are the high gain obtained with a compact multi-pass design and the excellent properties at 500 W output. Both, energy and pointing stability are at the level of one percent RMS fluctuations or below. Furthermore, the beam is of remarkable spatial quality, the M2 of the compressed 500 W output is 1.1 in both directions. A high stability is essential since we split off a small fraction of the Yb beam at an early stage for seed generation via white light generation in a YAG plate. A total of only 16 m beam path through amplifier & compressor will enable to use the same oscillator pulse for self-seeding and final pumping. Since we aim to derive 2-cycle IR pulses directly from the ps pump laser, first experimental results of 100 fold VIS pulse compression (10 fs @ 700 nm) and subsequent difference frequency generation (DFG) will be presented. The spectrum achieved via DFG supports 2-cycle duration at 2 µm wavelength.
References [1] Schmidt et al, “Decoupling Frequencies, Amplitudes and Phases in Nonlinear Optics,” Sci. Rep. 7, 7861 (2017). [2] B. E. Schmidt et al., “Frequency domain optical parametric amplification.” Nat. Commun. 5, 3643 (2014). [3] Gruson et al., “2.5 TW, two-cycle IR laser pulses via frequency domain optical parametric amplification”, OE 25, 27706 (2017)
103 Wednesday
High Harmonic Generation in Tailored Solids
Murat Sivis1,2, Marco Taucer1, Giulio Vampa1, Kyle Johnston1, André Staudte1, Andrei Yu. Naumov1, David M. Villeneuve1, Claus Ropers2, Paul B. Corkum1 1Joint Attosecond Science Laboratory, National Research Council of Canada and University of Ottawa, Canada 24th Physical Institute - Solids and Nanostructures, Georg-August University, Göttingen 37077, Germany [email protected]
Over the past three decades, high harmonic generation has enabled a new branch of science at attosecond timescales with powerful applications for extreme-ultraviolet and soft X-ray spectroscopy [1]. In that time, the generation of high harmonics has taken place almost exclusively in gas-phase targets. A great leap forward has gotten underway in the last few years, since harmonic generation was demonstrated in the solid-state [2]. In this study, we have explored new opportunities to tailor the emission of high harmonics from nanofabricated semiconductor targets, by controlling the structure and local composition of the generating medium [3]. Structured targets have an important influence on the driving field. Micron-scale wedges and cones confine and enhance the infrared driver, leading to up to a 1000-fold increase in harmonic emission from confined hotspots. Equally importantly, anisotropic structures exhibit an effective birefringence. Since high harmonic generation is sensitive to driving ellipticity, engineering the birefringence of the generating medium provides an important way to control the emission of high-order harmonics. In a second approach, we demonstrate an integrated Fresnel-zone-plate pattern that is ion-implanted in a silicon wafer. In this configuration, the solid target acts as a source for coherent ultraviolet radiation which is self-focused to diffraction-limited spot sizes. This indicates the possibility to bridge high-harmonic technology with silicon photonics, by demonstrating that the intensity distribution as well as the emission phase and polarization of the harmonic wave field can be controlled during the generation process in the tailored solid target. Structured and modified solid targets can allow complex states of extreme-ultraviolet light, similar to what is already possible in the visible or infrared spectral range [4]. High-harmonic generation is additionally sensitive to electric fields, which opens the door for optoelectronic devices. The introduction of solid-state fabrication techniques to this field may lead to a new class of devices for tailored high harmonic wave fields. The tools of nanofabrication can be used to precisely tailor the structure and composition of solid-state high harmonic targets. Utilizing these approaches to control and enhance high harmonic emission has the potential to enable a new generation of high harmonic devices. As a first example, we have demonstrated a Fresnel-zone target which focuses the emitted harmonics. Other applications of these techniques will ultimately open the door to high harmonic optoelectronics, and other applications for extreme-ultraviolet photonics.
References [1] P. B. Corkum and F. Krausz, “Attosecond science”, Nat. Phys. 3, 381–387 (2007). [2] S. Ghimire et al., “Observation of high-order harmonic generation in a bulk crystal” Nat. Phys. 7, 138–141 (2011). [3] M. Sivis et al., “Tailored Semiconductors for High-Harmonic Optoelectronics”, Science 357, 303-306 (2017). [4] X. Cai et al., “Integrated compact optical vortex beam emitters” Science 338, 363-366 (2012).
104 Wednesday
Strong-Field-Induced Vibronic Coupling
Michael Spanner National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, Canada [email protected]
Strong laser fields can significantly distort the electronic wave functions of atoms and molecules. When the field-free molecule possesses symmetries, the laser-induced spatial distortion of the electronic wave functions couples field-free electronic states of different symmetries. It is shown in this talk that this symmetry mixing gives rise to strong-field-induced vibronic couplings (i.e. derivative and scalar non- Born-Oppenheimer couplings) that would have been zero by symmetry in the field-free case. Formally, these couplings are the non-Born-Oppenheimer components of the polarizability interaction. A new field- dependent coupling term, similar in origin to the Stark-shift term, is derived that allows one to conveniently include the field-induced vibronic effects into time-dependent Schrödinger equation (TDSE) + simulations. Using N2 as a test case it is shown that, when active, these strong-field-induced vibronic couplings can be comparable in strength to multiphoton transitions caused by the standard laser-induced dipole couplings.
105 Wednesday
Is there a gauge-independent formulation of interband and intraband currents in solids?
Marco Taucer, Guilmot Ernotte, André Staudte, Paul B. Corkum Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, Ottawa, ON, Canada, K1A 0R6 [email protected]
As part of the search for an underlying physical picture of the harmonic generation process in solids, much attention has been focused on the question of interband and intraband processes. This conceptual separation is appealing in part because the interband picture bears a strong similarity to the well- understood gas-phase model [1,2], while the intraband picture is qualitatively different and unique to the solid state. Experiments have access to the emitted harmonics – their spectral intensity and phase – which reflect both the interband and intraband contributions, whatever their relative weight may be [3,4]. For now, a clean separation is only possible in calculations. Recently, however, it was shown that this separation may be gauge-dependent [5]. That is, a different choice of the gauge (which should leave all physical quantities unchanged) leads to different values for the intraband and interband currents. The total current, which relates to the experimentally observable harmonic spectrum, however, is not gauge- dependent. This raises the question of whether this conceptual decomposition of the current is well- defined. Is the interband current an observable? Other quantities may also be easy to calculate, but hard to access in experiments. An example is the instantaneous band population. We will show that the instantaneous populations can be gauge-dependent in precisely the same way as the separation of currents into their inter- and intra-band components. This raises the question of the significance of the instantaneous band populations. This poster will explore the definitions of these quantities. We ask whether or not it is possible to define the instantaneous band populations, and the interband and intraband currents, in a gauge-independent way. Such a definition would remove any ambiguity with respect to the choice of gauge.
References [1] Corkum, P. B. “Plasma perspective on strong field multiphoton ionization,” Phys. Rev. Lett. 71, 1994 (1993). [2] Vampa, G. et al. “Semiclassical analysis of high harmonic generation in bulk crystals,” Phys. Rev. B 91, 064302 (2015). [3] Vampa, G. et al. “Linking high harmonics from gases and solids,” Nature 522, 462-464 (2015). [4] Luu, T. T. et al. “Extreme ultraviolet high-harmonic spectroscopy of solids,” Nature 521, 498-502 (2015). [5] Földi, P. “Gauge invariance and interpretation of interband and intraband processes in high-order harmonic generation from bulk solids,” Phys. Rev. B 96, 035112 (2017).
106 Wednesday
15 W, few-cycle and ultra-stable mid-IR OPCPA
Nicolas Thiré1, Raman Maksimenka1, Balint Kiss2, Sebastian Jarosch3, Clément Ferchaud1, Pierre Bizouard1, Vittorio di Pietro1, Eric Cormier2, Karoly Osvay2, and Nicolas Forget1 1Fastlite, 1900 route des crêtes 06560 Valbonne, Sophia Antipolis, France 2ELI-HU Non-Profit Ltd, Dugonics tér 1, 6720 Szeged, Hungary 3Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom [email protected]
The extension of High order Harmonic Generation (HHG) towards XUV and up to soft-x-rays arises from the up-to-date development of driving sources with specific properties: mid-infrared wavelength, few- cycle pulses, high peak intensity, carrier-envelope phase stability and control, high energy and/or high- repetition.
Figure 1. Measured CEP drift over 8h. Average CEP drift is 0 mrad with an RMS value of 65 mrad over 8h (single-shot, 10 kHz). Inset: near field beam profile During the conference we will present experimental results of the system recently installed at the ELI- ALPS facility in Szeged (Hungary). It is a supercontinuum-seeded optical parametric chirped-pulse amplifier (OPCPA) generating few cycle pulses around 3.2 µm and optimized for long-term CEP-stability (cf. Fig. 1). This source now delivers 152-µJ, 39-fs pulses at 100 kHz repetition rate, which corresponds to a peak power of ~1 GW, an average power of 15.2 W and a pulse duration slightly under four optical cycles [1, 2]. The novelties of the system are: (i) Self-seeded OPCPA pumped with a diode-pumped solid-state laser delivering 1-ps pulses at 100 kHz, (ii) Bulk dispersion management through chirp-reversal by a 100-kHz acousto-optic pulse shaper, (iii) Record pulse duration of 39 fs at ~3.2 µm without post-compression stage at this average power (15.2 W, rms=0.7 % over 12h), (iv) Record non-averaged CEP stability with a phase noise as low as 65 mrad rms over more than 2.88 billion pulses (8 h at 100 kHz). To date this is the best recorded non-averaged CEP stability for an amplified system, independently of the wavelength, pulse duration or repetition rate [3], see Figure 1. Additional measurements have been performed, such as spatial quality (Strehl Ratio = 0.82, M2=1.4, near and far field beam profile – see inset of Fig1.), energy, pulse duration and spectrum pulse to pulse stability, that will be presented during the conference.
References [1] N. Thiré et al, “4-W, 100-kHz, few-cycle mid-infrared source with sub-100-mrad carrier-envelope phase noise”, Opt. Express, 25, 2 1505 (2017) [2] N. Thiré et al, submitted [3] F. Lücking et al, “Approaching the limits of carrier-envelope phase stability in a millijoule-class amplifier,” Opt. Lett. 39, 3884-3887 (2014).
107 Wednesday
Visualization of multiple bands structures in solids
Ayelet Julie Uzan*, Gal Orenstein*, Talia A. Parpar, Barry Bruner, Valerie Blanchet and Nirit Dudovich Department of Complex Systems, Weizmann Institute of Science, 76100 Rehovot, Israel [email protected]
High-harmonic generation in bulk crystal is attributed to the sub-cycle electronic motion driven by an intense laser field. Measuring HHG in crystals provides a unique insight into both sub-cycle electrons dynamics as well as the band structure of the solid. We study the internal dynamics in MgO crystal by generating high harmonics using 1300 nm laser field and its second harmonic field. Our measurement reveals multiple band excitations, probing the internal dynamics with attosecond precision. Furthermore, we find a direct link between the band structure and the spectral shape of the harmonics. This measurement establishes a new approach to visualize multiple band structure via high harmonic spectroscopy.
References [1] David A. Reis and Shambhu Ghimire, “Anisotropic high harmonic generation in bulk crystals,” Nature Physics, 13, 345-349 (2017). [2] Mette B. Gaarde, “Orientation dependence of temporal and spectral properties of high order harmonics in solids,” PRA, 96, 063412 (2017).
108 Wednesday
Disentangling Intracycle Interferences in Photoelectron Momentum Distributions Using Orthogonal Two-Color Laser Fields
Tian Wang2, Xinhua Xie1, ShaoGang Yu3, XuanYang Lai3, Stefan Roither1, Daniil Kartashov1, Andrius Baltuška1, XiaoJun Liu3*, Andre Staudte2†, and Markus Kitzler1‡ 1Photonics Institute, Technische Universität Wien, 1040 Vienna, Austria 2Joint Laboratory for Attosecond Science of the National Research Council and the University of Ottawa, Ottawa, Ontario K1A 0R6, Canada 3State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China *[email protected] †[email protected] ‡[email protected]
We use orthogonally polarized two-color (OTC) laser pulses to separate quantum paths in the multiphoton ionization of Ar atoms. Our OTC pulses consist of 400 and 800 nm light at a relative intensity ratio of 10:1. We find a hitherto unobserved interference in the photoelectron momentum distribution, which exhibits a strong dependence on the relative phase of the OTC pulse. Analysis of model calculations reveals that the interference is caused by quantum pathways from nonadjacent quarter cycles.
References [1] Markus Kitzler, Matthias Lezius, “Spatial Control of Recollision Wave Packets with Attosecond Precision” PRL 95, 253001 (2005). [2] Li Zhang, Xinhua Xie, et al. “Laser-sub-cycle two-dimensional electron-momentum mapping using orthogonal two-color fields” PRA 90, 061401(R) (2014). [3] Li Zhang, Xinhua Xie, et al. “Subcycle Control of Electron-Electron Correlation in Double Ionization” PRL 112, 193002 (2014) [4] Marko Haertelt, Xue-Bin Bian, et al. “Probing Molecular Dynamics by Laser-Induced Backscattering Holography” PRL 116, 133001 (2016).
[5] Xiaochun Gong, Peilun He, et al. “Two-Dimensional Directional Proton Emission in Dissociative Ionization of H2” PRL 113, 203001 (2014). [6] Martin Richter, Maksim Kunitski, et al. “Streaking Temporal Double-Slit Interference by an Orthogonal Two-Color Laser Field” PRL 114, 143001 (2015)
109 Wednesday
Generation of Few-Cycle UV pulses Synchronized with Attosecond XUV Pulses
V. Wanie1,2,*, M. Galli2,3, E. P. Månsson4, F. Frassetto5, L. Poletto5, F. Légaré1, M. Nisoli2,3 and F. Calegari2,4,6,* 1Institut National de la Recherche Scientifique, 1650 Blvd. Lionel-Boulet, J3X 1S2, Varennes (Qc), Canada 2Institute for Photonics and Nanotechnologies CNR-IFN, P.za Leonardo da Vinci 32, 20133 Milano, Italy 3Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy 4Center for Free-Electron Laser Science, DESY, Notkestr. 85, 22607 Hamburg, Germany 5Institute for Photonics and Nanotechnologies CNR-IFN, Via Trasea 7, 35131 Padova, Italy 6Physics Department, University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany *[email protected]; [email protected]
We developed an attosecond beamline combining XUV-attosecond and few-femtosecond ultraviolet pulses. The UV spectral range is of significant importance for a number of conjugated systems including biomolecules, for which ultrafast electronic dynamics have barely been explored [1]. We aim to study UV-induced electron dynamics in resonantly excited DNA/RNA building blocks using covariance spectroscopy. For this purpose a new reflectron-type mass spectrometer has been designed to provide a high-resolution for heavy ions and will be combined with a velocity map imaging spectrometer for covariance measurements [2]. A compact in-line XUV spectrometer is also integrated into the beamline. The ultraviolet light is obtained from the third harmonic generation (THG) of a 1 kHz Ti:Sapphire laser system post-compressed to 5 fs using an hollow-core fiber setup. We use a highly pressurized glass cell with a 400 m diameter in combination with a three stages differential pumping system and obtain up to ~200 nJ of UV light from 250 uJ of NIR. Fig. 1(a) shows the obtained spectrum and corresponding transform limit (b) of 1.1 fs (FWHM). Cross correlation measurements between the NIR and UV pulses indicate a pulse duration below 10 fs. A few combinations of gases, focusing optics and cell length have been investigated. Fig.1 (c) illustrates an example of the UV energy scaling with gas pressure. A recirculation system has been built in order to recycle the important amount of gas consumed for the generation.
Figure 1: (a) Spectrum from the Ti:Sapphire third harmonic generation supporting a 1.1 fs (FWHM) transform limited pulse duration (b). (c) Energy scaling for the THG with a ƒ = −50 cm mirror using argon and neon as generating media.
References [1] F. Calegari et al., Ultrafast electron dynamics in phenylalanine initiated by attosecond pulses. Science 346, 336–339 (2014). [2] O. Kornilov et al., Coulomb explosion of diatomic molecules in intense XUV fields mapped by partial covariance. J. Phys. B At. Mol. Opt. Phys. 46 (2013).
110
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AFS - Active Fiber Systems GmbH | Wildenbruchstraße 15 | 07745 Jena | Germany [email protected] | www.afs-jena.de | Office +49 3641 6338902 | Technical Support +49 3641 6338903 | Fax +49 3641 6338904 Please visit us in the exhibition area!
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[1] “Hollow-Core-Waveguide Compression of 22-mJ 3.9-μm Pulses ”, T. Balciunas, et al., AW1A.7 Lasers Congress (2016) [4] “Polarization-assisted amplitude gating as a route to tunable, high-contrast attosecond pulses”, H. R. Timmers, et al., Optica, 3, 707 (2016) [2] ”Hollow-core-waveguide compression of multi-millijoule CEP-stable 3.2 μm pulses”G. Fan, et al., Optica 3, 1308 (2016) [5] ”Generating high contrast, near single-cycle waveforms with third order dispersion compensation”, H. R. Timmers, et al., OL, 42, 811 (2017) [3] “Simple fiber-based solution for coherent multi-dimensional spectroscopy in the visible regime”, H. Seiler, et al., OL, 42, 643, (2017) [6] “Direct compression of 170-fs 50-cycle pulses down to 1.5 cycles ”, Y. Jeong et al., in preparation (2018)
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UltraFast Innovations provides customized premium ultrafast optics and devices. Many years of know-how in optics design and manufacturing allow us to implement latest research results into novel optics solutions. Our optics can be found in the laser sources of most major femtosecond OEM manufacturers. Our optics portfolio features: Ultra- broadband mirrors for pulse compression down to our hollow core fiber compressor combines optimum fiber coupling in an ultra-stable setup with our unique PC70 chirped mirrors for best available pulse compression results, making it a versatile tool for applications ranging from attosecond pulse generation to OPCPA seeding and 2D electronic spectroscopy. The hollow core fiber compressor is ideal to generate intense few-cycle pulses with ultrabroad bandwidth from the output of Ti:Sa amplifiers. The output pulse duration of laser amplifiers is limited by gain narrowing to about 20 fs, and shorter pulses can only be reached with additional spectral broadening. Our hollow core fiber compressor couples the laser output with high efficiency into a noble-gas filled glass capillary, where nonlinear interaction broadens the input pulses. With our optimized design extreme spectral broadening to a coverage of up to 270-1000 nm. Pulses after the fiber are compressed with our PC70 ultra-broadband chirped mirrors featuring our proprietary double-angle technology for the best available pulse-compression performance. As extensions to the hollow core fiber compressor we can provide an input beam stabilization module, a gas and vacuum handling system, and variable GDD management. Combining the reliability of spectrally resolved detection with an ultrabroad spectral coverage of up to 250-2100 nm makes our White Light Interferometer the ideal instrument for ultrafast optics characterization and quality control. Our White Light Interferometer uses spectrally resolved interferometry to accurately measure the Group Delay Dispersion (GDD) of multi-layer ultrafast optics. The device has been developed at the Max-Planck Institute for Quantum Optics (Garching, Germany) to characterize and refine some of the most advanced coatings to date. Combining spectral with temporal information and the possibility to accumulate multiple passes over the same optic ensures reliable results with unique spectral coverage of up to 250-1100 nm (UV/vis/NIR version) and 900-2100 nm (IR version). Spectrally resolved detection makes reference lasers together with any related test sample restrictions on specific reflection or transmission bands obsolete. This opens the full spectral range to characterize even ultra-broadband or advanced narrowband coatings. The flexible optical setup can measure mirrors and transparent samples under angles of incidence variable between 0 and 70 degrees. Our reflectometer uses the extreme sensitivity of cavity ring-down spectroscopy to quantify the losses of advanced optical coatings at the limits of current fabrication methods. Conventional absorption and reflection measurements are not sufficiently sensitive to quantify today´s super-reflective mirror coatings and are typically limited to the > 1000 ppm range (corresponding to < 99.9 % reflectivity). Our device increases measurement sensitivity by incorporating the test sample into an optical cavity and measures losses as an intensity ring-down in time domain. With this technique the device quantifies losses down to 5 ppm and thus makes for example characterization of ultra-high reflective mirrors with up to 99.9995 % reflectivity possible. We also provide specialized diagnostic and instrumentation for ultrafast applications. Our extreme ultraviolet grazing- incidence flat field spectrometer features a unique modular design that allows to cover a full spectral range of 5-80 nm with a single grating. The spectrograph uses aberration-corrected flat-field imaging in combination with a CCD or MCP detector to record full spectra without the need for wavelength scanning. Its grazing incidence geometry maximizes efficiency in this delicate spectral region. In conventional spectrograph designs the entrance slit is a bottleneck limiting light flux and flexibility. Our spectrograph goes one step further and can be used also without any entrance slit, directly imaging the XUV or VUV light source for a variety of source distances. Its modular design is able to match different experimental geometries and configurations. It features an integrated slit holder, gate valve and filter insertion unit, as well as motorized grating positioning along 3 axes. The XUV spectrograph covers a spectral range of up to 1-80 nm (1240-15.5 eV). The VUV spectrograph provides a complementary coverage of 70-200 nm (17.7-6.2 eV). Our third-order autocorrelator measures laser pulse contrast with the highest commercially available dynamic range of up to 12 orders of magnitude. This extreme level of sensitivity allows to identify even lowest background signals and trace tiniest pre- and post-pulse replica for high-field experiments and plasma physics. Its sequential scheme with all- reflective optics ensures measurements without the typical ghost-pulse artefacts. The Tundra reaches its spectacular sensitivity already at 100-200 µJ input energy, making it possible for complex laser systems to search the sources of background contamination already in low-energy stages. The autocorrelator is available for 800 nm and 1030 nm, for a huge range of pulse durations from <20 fs to several picoseconds. With its unique delay range of up to 4 ns the Tundra can find even strongly displaced pre-pulses rising in laser amplification stages from components like Pockels cells or the like.
UltraFast Innovations GmbH Dr. Hans Koop Am Coulombwall 1 85748 Garching Email. [email protected]
Time Monday, May 7 Tuesday, May 8 Wednesday, May 9 Thursday, May 10 Friday, May 11 Tu1x We1x Th1x Fr1x Chair: F. Légaré Chair: B. Bergues Chair: M. Kübel Chair: J. Levesque 8:30 D.M. Villeneuve J. Marangos G.G. Paulus O. Smirnova -9:50 R. Bhardwaj H. Niikura N. Dudovich K. Lee E.Constant Z. Chang M. Kling A.D. Bandrauk 9:50 Coffee Break Coffee Break Coffee Break Coffee Break -10:20 Tu2x We2x Th2x Fr2x Chair: T.J. Hammond Chair: M. Sivis Chair: M. Meckel Chair: H. Ibrahim 10:20 J.-C. Diels C. Ropers P. Bucksbaum K. Midorikawa -12:00 K.T. Kim D. Zeidler H. Stapelfeldt H. Akagi I. Litvinyuk J. Peng A.Fleischer C. Trallero C.H. Nam P. Berini R. Dörner G. Mourou NRC lab tours 12:00 G. Leuchs -12:30 Lunch Lunch Lunch 12:30 Lunch -13:30 and Tu3x Th3x Fr3x Chair: E. Karimi Chair: G. Vampa Chair: D.M.Villeneuve 13:30 Arrival P. Brumer X. Wang M.Yu. Ivanov -15:30 R. Boyd A. Emmanouilidou M. Scully J.B. Bertrand T. Brabec F. Krausz M.Piché free discussion M. Spanner P.B. Corkum 15:30 Coffee Break and Coffee Break Coffee Break -16:00 Tu4x breakout groups Th4x Chair: A. Shiner Chair: L. Arissian 16:00 M. Vrakking S. Leone -18:00 D. Strickland H. Schmidt-Böcking J.-C. Kieffer S.-L. Chin S. Patchkovskii A. Stolow 18:00 Departure free time -19:00 free time free time 19:00 Conference Dinner -20:00 keynotes by Welcome M. Nemer 20:00 Reception Poster session Poster session -21:30 G. Tanguay J. Alcock